CHAPTER IX--RETROSPECT AND PROSPECT

The scientific attitude of mind, p. 2 30--Natural versus supernatural,

p. 233--Inductive versus deductive reasoning, p. 235--Logical induction

versus hasty generalization, p. 239--The future of Darwinism, p. 241.

APPENDIX

A LIST OF SOURCES

A HISTORY OF SCIENCE--BOOK V

ASPECTS OF RECENT SCIENCE

STUDENTS of the classics will recall that the old Roman historians were

accustomed to detail the events of the remote past in what they were

pleased to call annals, and to elaborate contemporary events into

so-called histories. Actuated perhaps by the same motives, though with

no conscious thought of imitation, I have been led to conclude this

history of the development of natural science with a few chapters

somewhat different in scope and in manner from the ones that have gone

before.

These chapters have to do largely with recent conditions. Now and again,

to be sure, they hark back into the past, as when they tell of the

origin of such institutions as the British Museum, the Royal Society,

and the Royal Institution; or when the visitor in modern Jena imagines

himself transplanted into the Jena of the sixteenth century. But these

reminiscent moods are exceptional. Our chief concern is with strictly

contemporary events--with the deeds and personalities of scientific

investigators who are still in the full exercise of their varied powers.

I had thought that such outlines of the methods of contemporary workers,

such glimpses of the personalities of living celebrities, might form a

fitting conclusion to this record of progress. There is a stimulus in

contact with great men at first hand that is scarcely to be gained in

like degree in any other way. So I have thought that those who have not

been privileged to visit the great teachers in person might like to

meet some of them at second hand. I can only hope that something of

the enthusiasm which I have gained from contact with these men may make

itself felt in the succeeding pages.

It will be observed that these studies of contemporary workers are

supplemented with a chapter in which a hurried review is taken of the

field of cosmical, of physical, and of biological science, with

reference to a few of the problems that are still unsolved. As we have

noted the clearing up of mystery after mystery in the past, it may be

worth our while in conclusion thus to consider the hordes of mysteries

which the investigators of our own age are passing on to their

successors. For the unsolved problems of to-day beckon to the alluring

fields of to-morrow.

I. THE BRITISH MUSEUM

IN the year 1753 a remarkable lottery drawing took place in London.

It was authorized, through Parliament, by "his gracious Majesty" King

George the Second. Such notables as the archbishop of Canterbury and the

lord chancellor of the realm took official interest in its success. It

was advertised far and wide--as advertising went in those days--in the

_Gazette_, and it found a host of subscribers. Of the fifty thousand

tickets--each costing three pounds--more than four thousand were to

be of the class which the act of Parliament naively describes as

"fortunate tickets." The prizes aggregated a hundred thousand pounds.

To be sure, state lotteries were no unique feature in the England of

that day. They formed as common a method of raising revenue in the

island realm of King George II. as they still do in the alleged

continental portion of his realm, France, and in the land of his

nativity, Germany. Indeed, the particular lottery in question was to

be officered by the standing committee on lotteries, whose official

business was to "secure two and a half million pounds for his Majesty"

by this means. But the great lottery of 1754 had interest far beyond the

common run, for it aimed to meet a national need of an anomalous kind--a

purely intellectual need. The money which it was expected to bring was

to be used to purchase some collections of curiosities and of books that

had been offered the government, and to provide for their future care

and disposal as a public trust for the benefit and use of the people.

The lottery brought the desired money as a matter of course, for the

"fool's tax" is the one form of revenue that is paid without stint and

without grumbling. Almost fifty thousand pounds remained in the hands

of the archbishop of Canterbury and his fellow-trustees after the prizes

were paid. And with this sum the institution was founded which has been

increasingly famous ever since as the British Museum.

The idea which had this splendid result had originated with Sir Hans

Sloane, baronet, a highly respected practising physician of Chelsea,

who had accumulated a great store of curios, and who desired to see the

collection kept intact and made useful to the public after his death.

Dying in 1753, this gentleman had directed in his will that the

collection should be offered to the government for the sum of twenty

thousand pounds; it had cost him fifty thousand pounds. The government

promptly accepted the offer--as why should it not, since it had at hand

so easy a means of raising the necessary money? It was determined to

supplement the collection with a library of rare books, for which

ten thousand pounds was to be paid to the Right Honorable Henrietta

Cavendish Holies, Countess of Oxford and Countess Mortimer, Relict of

Edward, Earl of Oxford and Earl Mortimer, and the Most Noble Margaret

Cavendish, Duchess of Portland, their only daughter.

The purchases were made and joined with the Cottonian library, which

was already in hand. A home was found for the joint collection, along

with some minor ones, in Montague Mansion, on Great Russell Street, and

the British Museum came into being. Viewed retrospectively, it seems

a small affair; but it was a noble collection for its day; indeed,

the Sloane collection of birds and mammals had been the finest private

natural history collection in existence. But, oddly enough, the weak

feature of the museum at first was exactly that feature which has been

its strongest element in more recent years--namely, the department of

antiquities. This department was augmented from time to time, notably by

the acquisition of the treasures of Sir William Hamilton in 1773; but it

was not till the beginning of the nineteenth century that the windfall

came which laid the foundation for the future incomparable greatness of

the museum as a repository of archaeological treasures.

In that memorable year the British defeated the French at Alexandria,

and received as a part of the conqueror's spoils a collection of

Egyptian antiquities which the savants of Napoleon's expedition had

gathered and carefully packed, and even shipped preparatory to sending

them to the Louvre. The feelings of these savants may readily be

imagined when, through this sad prank of war, their invaluable treasures

were envoyed, not to their beloved France, but to the land of their

dearest enemies, there to be turned over to the trustees of the British

Museum.

The museum authorities were not slow to appreciate the value of the

treasures that had thus fallen into their hands, yet for the moment

it proved to them something of a white elephant. Montague Mansion was

already crowded; moreover, its floors had never been intended to hold

such heavy objects, so it became imperatively necessary to provide new

quarters for the collection. This was done in 1807 by the erection of

a new building on the old site. But the trustees of that day failed to

gauge properly the new impulse to growth that had come to the museum

with the Egyptian antiquities, for the new building was neither in

itself sufficient for the needs of the immediate future nor yet

so planned as to be susceptible of enlargement with reasonable

architectural effect. The mistakes were soon apparent, but, despite

various tentatives and "meditatings," fourteen years elapsed before

the present magnificent building was planned. The construction, wing by

wing, began in 1823, but it was not until 1846 that the last vestige

of the old museum buildings had vanished, and in their place, spreading

clear across the spacious site, stood a structure really worthy of the

splendid collection for which it was designed.

But no one who sees this building to-day would suspect its relative

youth. Half a century of London air can rival a cycle of Greece or Italy

in weathering effect, and the fine building of the British Museum

frowns out at the beholder to-day as grimy and ancient-seeming as if

its massive columns dated in fact from the old Grecian days which they

recall. Regardless of age, however, it is one of the finest and most

massive specimens of Ionic architecture in existence. Forty-four massive

columns, in double tiers, form its frontal colonnade, jutting forward

in a wing at either end. The flight of steps leading to the central

entrance is in itself one hundred and twenty-five feet in extent; the

front as a whole covers three hundred and seventy feet. Capping the

portico is a sculptured tympanum by Sir Richard Westmacott, representing

the "Progress of Civilization" not unworthily. As a whole, the building

is one of the few in London that are worth visiting for an inspection of

their exterior alone. It seems admirably designed to be, as it is, the

repository of one of the finest collections of Oriental and classical

antiquities in the world.

There is an air of repose about the _ensemble_ that is in itself

suggestive of the Orient; and the illusion is helped out by the pigeons

that flock everywhere undisturbed about the approaches to the building,

fluttering to be fed from the hand of some recognized friend, and

scarcely evading the feet of the casual wayfarer. With this scene before

him, if one will close his ears to the hum of the great city at his

back he can readily imagine himself on classical soil, and, dreaming of

Greece and Italy, he will enter the door quite prepared to find himself

in the midst of antique marbles and the atmosphere of by-gone ages.

I have already pointed out that the turning-point in the history of

the British Museum came just at the beginning of the century, with the

acquisition of the Egyptian antiquities. With this the institution threw

off its swaddling-clothes. Hitherto it had been largely a museum of

natural history; in future, without neglecting this department, it

was to become equally important as a museum of archaeology. The Elgin

marbles, including the wonderful Parthenon frieze, confirmed this

character, and it was given the final touch by the reception, about

the middle of the century, of the magnificent Assyrian collection just

exhumed at the seat of old Nineveh by Mr. (afterwards Sir Henry) Layard.

Since then these collections, with additions of similar character, have

formed by far the most important feature of the British Museum. But in

the mean time archaeology has become a science.

Within recent years the natural history collection has been removed _in

toto_ from the old building to a new site far out in South Kensington,

and the casual visitor is likely to think of it as a separate

institution. The building which it occupies is very modern in appearance

as in fact. It is a large and unquestionably striking structure, and one

that gives opportunity for very radical difference of opinion as to its

architectural beauty. By some it is much admired; by others it is almost

equally scoffed at. Certain it is that it will hardly bear comparison

with the parent building in Great Russell Street.

Interiorly, the building of the natural history museum is admirably

adapted for its purpose. Its galleries are for the most part well

lighted, and the main central hall is particularly well adapted for

an exhibition of specimens, to which I shall refer more at length in

a moment. For the rest there is no striking departure from the

conventional. Perhaps it is not desired that there should be, since long

experience seems to have settled fairly well the problem of greatest

economy of space, combined with best lighting facilities, which always

confronts the architect in founding a natural history museum.

There is, however, one striking novel feature in connection with the

structure of the natural history museum at Kensington which must not

be overlooked. This is the quite unprecedented use of terra-cotta

ornamentation. Without there is a striking display of half-decorative

and half-realistic forms; while within the walls and pillars everywhere

are covered with terracotta bas-reliefs representing the various forms

of life appropriate to the particular department of the museum which

they ornament. This very excellent feature might well be copied

elsewhere, and doubtless will be from time to time.

As to the exhibits proper within the museum, it may be stated in a word

that they cover the entire range of the faunas and floras of the

globe in a variety and abundance of specimens that are hardly excelled

anywhere, and only duplicated by one or two other collections in Europe

and two or three in America.

It would be but a reiteration of what the catalogues of all large

collections exhibit were one to enumerate the various forms here shown,

but there are two or three exhibits in this museum which are more novel

and which deserve special mention. One of these is to be found in a set

of cases in the main central hall. Here are exhibited, in a delightfully

popular form, some of the lessons that the evolutionist has taught us

during the last half-century. Appropriately enough, a fine marble statue

of Darwin, whose work is the fountain-head of all these lessons, is

placed on the stairway just beyond, as if to view with approval this

beautiful exemplification of his work.

One of these cases illustrates the variations of animals under

domestication, the particular specimens selected being chiefly the

familiar pigeon, in its various forms, and the jungle-fowl with its

multiform domesticated descendants.

Another case illustrates very strikingly the subject of protective

coloration of animals. Two companion cases are shown, each occupied by

specimens of the same species of birds and animals--in one case in their

summer plumage and pelage and in the other clad in the garb of winter.

The surroundings in the case have, of course, been carefully prepared

to represent the true environments of the creatures at the appropriate

seasons. The particular birds and animals exhibited are the

willow-grouse, the weasel, and a large species of hare. All of these,

in their summer garb, have a brown color, which harmonizes marvellously

with their surroundings, while in winter they are pure white, to match

the snow that for some months covers the ground in their habitat.

The other cases of this interesting exhibit show a large variety of

birds and animals under conditions of somewhat abnormal variation, in

the one case of albinism and the other of melanism. These cases are,

for the casual visitor, perhaps the most striking of all, although, of

course, they teach no such comprehensive lessons as the other exhibits

just referred to.

The second of the novel exhibits of the museum to which I wish to refer

is to be found in a series of alcoves close beside the central cases in

the main hallway.

Each of these alcoves is devoted to a class of animals--one to mammals,

one to birds, one to fishes, and so on. In each case very beautiful sets

of specimens have been prepared, illustrating the anatomy and physiology

of the group of animals in question. Here one may see, for example, in

the alcove devoted to birds, specimens showing not only details of

the skeleton and muscular system, but the more striking examples of

variation of form of such members as the bill, legs, wings, and tails.

Here are preparations also illustrating, very strikingly, the vocal

apparatus of birds. Here, again, are finely prepared wings, in which

the various sets of feathers have been outlined with different-colored

pigments, so that the student can name them at a glance. In fact, every

essential feature of the anatomy of the bird may be studied here as in

no other collection that I know of. And the same is true of each of the

other grand divisions of the animal kingdom. This exhibit alone gives an

opportunity for the student of natural history that is invaluable. It is

quite clear to any one who has seen it that every natural history museum

must prepare a similar educational exhibit before it can claim to do

full justice to its patrons.

A third feature that cannot be overlooked is shown in the numerous cases

of stuffed birds, in which the specimens are exhibited, not merely

by themselves on conventional perches, but amid natural surroundings,

usually associated with their nests and eggs or young. These exhibits

have high artistic value in addition to their striking scientific worth.

They teach ornithology as it should be taught, giving such clews to

the recognition of birds in the fields as are not at all to be found in

ordinary collections of stuffed specimens. This feature of the museum

has, to be sure, been imitated in the American Museum of Natural History

in New York, but the South Kensington Museum was the first in the field

and is still the leader.

A few words should be added as to the use made by the public of the

treasures offered for their free inspection by the British Museum. I

shall attempt nothing further than a few data regarding actual visits to

the museum. In the year 1899 the total number of such visits

aggregated 663,724; in 1900 the figures rise to 689,249--well towards

three-quarters of a million. The number of visits is smallest in the

winter months, but mounts rapidly in April and May; it recedes slightly

for June and July, and then comes forward to full tide in August, during

which month more than ninety-five thousand people visited the museum

in 1901, the largest attendance in a single day being more than nine

thousand. August, of course, is the month of tourists--particularly of

tourists from America--but it is interesting and suggestive to note

that it is not the tourist alone who visits the British Museum, for the

flood-tide days of attendance are always the Bank holidays, including

Christmas boxing-day and Easter Monday, when the working-people turn out

_en masse_. On these days the number of visits sometimes mounts above

ten thousand.

All this, it will be understood, refers exclusively to the main building

of the museum on Great Russell Street. But, meantime, out in Kensington,

at the natural history museum, more than half a million visits each year

are also made. In the aggregate, then, about a million and a quarter of

visits are paid to the British Museum yearly, and though the bulk of the

visitors may be mere sight-seers, yet even these must carry away many

ideas of value, and it hardly requires argument to show that, as a

whole, the educational influence of the British Museum must be enormous.

Of its more direct stimulus to scientific work through the trained

experts connected with the institution I shall perhaps speak in another

connection.

II. THE ROYAL SOCIETY OF LONDON FOR IMPROVING NATURAL KNOWLEDGE

A SESSION OF THE SOCIETY

THERE is one scientific institution in London more venerable and more

famous even than the British Museum. This, of course, is the Royal

Society, a world-famous body, whose charter dates from 1662, but whose

actual sessions began at Gresham College some twenty years earlier. One

can best gain a present-day idea of this famous institution by attending

one of its weekly meetings in Burlington House, Piccadilly--a great,

castle-like structure, which serves also as the abode of the Royal

Chemical Society and the Royal Academy of Arts. The formality of an

invitation from a fellow is required, but this is easily secured by any

scientific visitor who may desire to attend the meeting. The

programme of the meeting each week appears in that other great British

institution, the _Times_, on Tuesdays.

The weekly meeting itself is held on Thursday afternoon at half-past

four. As one enters the door leading off the great court of Burlington

House a liveried attendant motions one to the rack where great-coat

and hat may be left, and without further ceremony one steps into the

reception-room unannounced. It is a middle-sized, almost square room,

pillared and formal in itself, and almost without furniture, save for

a long temporary table on one side, over which cups of tea are being

handed out to the guests, who cluster there to receive it, and then

scatter about the room to sip it at their leisure. We had come to hear

a lecture and had expected to be ushered into an auditorium; but we had

quite forgotten that this is the hour when all England takes its tea,

the _élite_ of the scientific world, seemingly, quite as much as the

devotees of another kind of society. Indeed, had we come unawares into

this room we should never have suspected that we had about us other than

an ordinary group of cultured people gathered at a conventional

"tea," except, indeed, that suspicion might be aroused by the great

preponderance of men--there being only three or four women present--and

by the fact that here and there a guest appears in unconventional

dress--a short coat or even a velvet working-jacket. For the rest

there is the same gathering into clusters of three or four, the same

inarticulate clatter of many voices that mark the most commonplace of

gatherings.

But if one will withdraw to an inoffensive corner and take a critical

view of the assembly, he will presently discover that many of the faces

are familiar to him, although he supposed himself to be quite among

strangers. The tall figure, with the beautiful, kindly face set in

white hair and beard, has surely sat for the familiar portrait of Alfred

Russel Wallace. This short, thick-set, robust, business-like figure is

that of Sir Norman Lockyer. Yonder frail-seeming scholar, with white

beard, is surely Professor Crookes. And this other scholar, with tall,

rather angular frame and most kindly gleam of eye, is Sir Michael

Foster; and there beyond is the large-seeming though not tall figure,

and the round, rosy, youthful-seeming, beautifully benevolent face of

Lord Lister. "What! a real lord there?" said a little American girl to

whom I enumerated the company after my first visit to the Royal Society.

"Then how did he act? Was he very proud and haughty, as if he could not

speak to other people?" And I was happy to be able to reply that though

Lord Lister, perhaps of all men living, would be most excusable did he

carry in his manner the sense of his achievements and honors, yet in

point of fact no man could conceivably be more free from any apparent

self-consciousness. As one watches him now he is seen to pass from group

to group with cordial hand-shake and pleasant word, clearly the most

affable of men, lord though he be, and president of the Royal Society,

and foremost scientist of his time.

Presently an attendant passed through the tearoom bearing a tremendous

silver mace, perhaps five feet long, surmounted by a massive crown and

cross, and looking like nothing so much as a "gigantic war-club."

This is the mace which, when deposited on the president's desk in the

lecture-room beyond, will signify that the society is in session. "It is

the veritable mace," some one whispers at your elbow, "concerning which

Cromwell gave his classical command to 'Remove that bauble.'" But since

the mace was not made until 1663, some five years after Cromwell's

death, this account may lack scientific accuracy. Be that as it may,

this mace has held its own far more steadily than the fame of its

alleged detractor, and its transportation through the tea-room is the

only manner of announcement that the lecture is about to open in the

hall beyond. Indeed, so inconspicuous is the proceeding, and so quietly

do the members that choose to attend pass into the lecture-hall, leaving

perhaps half the company engaged as before, that the "stranger "--as

the non-member is here officially designated--might very readily fail

to understand that the séance proper had begun. In any event, he cannot

enter until permission has been formally voted by the society.

When he is allowed to enter he finds the meeting-room little different

from the one he has left, except that it is provided with a sort of

throne on a raised platform at one end and with cushioned benches for

seats. On the throne, if one may so term it, sits Lord Lister, scarcely

more than his head showing above what seems to be a great velvet cushion

which surmounts his desk, at the base of which, in full view of the

society, rests the mace, fixing the eye of the "stranger," as it is

alleged to have fixed that of Cromwell aforetime, with a peculiar

fascination. On a lower plane than the president, at his right and left,

sit Sir Michael Foster and Professor Arthur William Rucker, the two

permanent secretaries. At Sir Michael's right, and one stage nearer the

audience, stands the lecturer, on the raised platform and behind the

desk which extends clear across the front of the room. As it chances,

the lecturer this afternoon is Professor Ehrlich, of Berlin and

Frankfort-on-the-Main, who has been invited to deliver the Croonian

lecture. He is speaking in German, and hence most of the fellows are

assisting their ears by following the lecture in a printed translation,

copies of which, in proof, were to be secured at the door.

The subject of the lecture is "Artificial Immunization from Disease."

It is clear that the reader is followed with interested attention, which

now and again gives rise to a subdued shuffle of applause.

The fact that the lecturer is speaking German serves perhaps to suggest

even more vividly than might otherwise occur to one the contrast between

this meeting and a meeting of the corresponding German society--the

Royal Academy of Sciences at Berlin. Each is held in an old building

of palatial cast and dimensions, of which Burlington House, here

in Piccadilly, is much the older--dating from 1664--although its

steam-heating and electric-lighting apparatus, when contrasted with the

tile stoves and candles of the other, would not suggest this. For the

rest, the rooms are not very dissimilar in general appearance, except

for the platform and throne. But there the members of the society are

shut off from the audience both by the physical barrier of the table and

by the striking effect of their appearance in full dress, while here the

fellows chiefly compose the audience, there being only a small company

of "strangers" present, and these in no way to be distinguished by dress

or location from the fellows themselves. It may be added that the custom

of the French Academy of Sciences is intermediate between these two.

There the visitors occupy seats apart, at the side of the beautiful

hall, the main floor being reserved for members. But the members

themselves are not otherwise distinguishable, and they come and go and

converse together even during the reading of a paper almost as if this

were a mere social gathering. As it is thus the least formal, the

French meeting is also by far the most democratic of great scientific

gatherings. Its doors are open to whoever may choose to enter. The

number who avail themselves of this privilege is not large, but it

includes, on occasions, men of varied social status and of diverse races

and colors--none of whom, so far as I could ever discern, attracts the

slightest attention.

At the German meeting, again, absolute silence reigns. No one thinks

of leaving during the session, and to make any sound above a sigh would

seem almost a sacrilege. But at the Royal Society an occasional auditor

goes or comes, there are repeated audible signs of appreciation of the

speaker's words, and at the close of the discourse there is vigorous

and prolonged applause. There is also a debate, of the usual character,

announced by the president, in which "strangers" are invited to

participate, and to which the lecturer finally responds with a brief

_Nachwort_, all of which is quite anomalous from the German or French

stand-points. After that, however, the meeting is declared adjourned

with as little formality in one case as in the others, and the fellows

file leisurely out, while the attendant speedily removes the mace, in

official token that the séance of the Royal Society is over.

THE LIBRARY AND READING-ROOM

But the "stranger" must not leave the building without mounting to the

upper floor for an inspection of the library and reading-room. The rooms

below were rather bare and inornate, contrasting unfavorably with the

elegant meeting-room of the French institute. But this library makes

full amends for anything that the other rooms may lack. It is one of the

most charming--"enchanting" is the word that the Princess Christian is

said to have used when she visited it recently--and perhaps quite the

most inspiring room to be found in all London. It is not very large as

library rooms go, but high, and with a balcony supported by Corinthian

columns. The alcoves below are conventional enough, and the high

tables down the centre, strewn with scientific periodicals in engaging

disorder, are equally conventional. But the color-scheme of the

decorations--sage-green and tawny--is harmonious and pleasing, and the

effect of the whole is most reposeful and altogether delightful.

Chief distinction is given the room, however, by a row of busts on

either side and by certain pieces of apparatus on the centre tables.

The busts, as will readily be surmised, are portraits of distinguished

fellows of the Royal Society. There is, however, one exception to this,

for one bust is that of a woman--Mary Somerville, translator of the

_Mécanique Céleste_, and perhaps the most popular of the scientific

writers of her time. It is almost superfluous to state that the row of

busts begins with that of Newton. The place of honor opposite is held by

that of Faraday. Encircling the room to join these two one sees, among

others, the familiar visages of Dr. Gilbert; of Sir Joseph Banks, the

famous surgeon of the early nineteenth century, who had the honor of

being the only man that ever held the presidential chair of the

Royal Society longer than it was held by Newton; of James Watts, of

"steam-engine" fame; of Sabine, the astronomer, also a president of

the society; and of Dr. Falconer and Sir Charles Lyell, the famous

geologists.

There are numerous other busts in other rooms, some of them stowed away

in nooks and crannies, and the list of those selected for the library

does not, perhaps, suggest that this is the room of honor, unless,

indeed, the presence of Newton and Faraday gives it that stamp. But in

the presence of the images of these two, and of Lyell, to go no farther,

one feels a certain sacredness in the surroundings.

If this is true of the mere marble images, what shall we say of the

emblems on the centre table? That little tubular affair, mounted on a

globe, the whole cased in a glass frame perhaps two feet high, is the

first reflecting telescope ever made, and it was shaped by the hand of

Isaac Newton. The brass mechanism at the end of the next table is the

perfected air-pump of Robert Boyle, Newton's contemporary, one of the

founders of the Royal Society and one of the most acute scientific minds

of any time. And here between these two mementos is a higher apparatus,

with crank and wheel and a large glass bulb that make it conspicuous.

This is the electrical machine of Joseph Priestley. There are other

mementos of Newton--a stone graven with a sun-dial, which he carved as

a boy, on the paternal manor-house; a chair, said to have been his,

guarded here by a silk cord against profanation; bits of the famous

apple-tree which, as tradition will have it, aided so tangibly in

the greatest of discoveries; and the manuscript of the _Principia_

itself--done by the hand of an amanuensis, to be sure, but with

interlinear corrections in the small, clear script of the master-hand

itself. Here, too, is the famous death-mask, so much more interesting

than any sculptured portrait, and differing so strangely in its

broad-based nose and full, firm mouth from the over-refined lineaments

of the sculptured bust close at hand. In a room not far away, to reach

which one passes a score or two of portraits and as many busts of

celebrities--including, by-the-bye, both bust and portrait of Benjamin

Franklin--one finds a cabinet containing other mementos similar to those

on the library tables. Here is the first model of Davy's safety-lamp;

there a chronometer which aided Cook in his famous voyage round the

world. This is Wollaston's celebrated "Thimble Battery." It will slip

readily into the pocket, yet he jestingly showed it to a visitor as

"his entire laboratory." That is a model of the double-decked boat made

by Sir William Petty, and there beyond is a specimen of almost, if not

quite, the first radiometer devised by Sir William Crookes.

As one stands in the presence of all these priceless relics, so vividly

do the traditions of more than two centuries of science come to mind

that one seems almost to have lived through them. One recalls, as if it

were a personal recollection, the founding of the Royal Society itself

in 1662, and the extraordinary scenes which the society witnessed during

the years of its adolescence.

As one views the mementos of Boyle and Newton, one seems to be living in

the close of the seventeenth century. It is a troublous time in England.

Revolution has followed revolution. Commonwealth has supplanted monarchy

and monarchy commonwealth. At last the "glorious revolution" of 1688 has

placed a secure monarch on the throne. But now one external war follows

another, and the new king, William of Orange, is leading the "Grand

Alliance" against the French despot Louis XIV. There is war everywhere

in Europe, and the treaty of Ryswick, in 1697, is but the preparation

for the war of the Spanish Alliance, which will usher in the new

century. But amid all this political turmoil the march of scientific

discovery has gone serenely on; or, if not serenely, then steadily, and

perhaps as serenely as could be hoped. Boyle has discovered the law of

the elasticity of gases and a host of minor things. Robert Hooke is

on the track of many marvels. But all else pales before the fact that

Newton has just given to the world his marvellous law of gravitation,

which has been published, with authority of the Royal Society, through

the financial aid of Halley. The brilliant but erratic Hooke lias

contested the priority of discovery and strenuously claimed a share in

it. Halley eventually urges Newton to consider Hooke's claim in some of

the details, and Newton yields to the extent of admitting that the

great fact of gravitational force varying inversely as the square of

the distance had been independently discovered by Hooke; but he includes

also Halley himself and Sir Christopher Wren, along with Hooke,

as equally independent discoverers of the same principle. To the

twentieth-century consciousness it seems odd to hear Wren thus named as

a scientific discoverer; but in truth the builder of St. Paul's began

life as a professor of astronomy at Gresham College, and was the

immediate predecessor of Newton himself in the presidential chair of the

Royal Society. Now, at the very close of the seventeenth century, Boyle

is recently dead, but Hooke, Wren, Halley, and Newton still survive:

some of them are scarcely past their prime. It is a wonderful galaxy of

stars of the first magnitude, and even should no other such names come

in after-time, England's place among the scientific constellations is

secure.

But now as we turn to the souvenirs of Cooke and Wollaston and Davy

the scene shifts by a hundred years. We are standing now in the closing

epoch of the eighteenth century. These again are troublous times. The

great new colony in the West has just broken off from the parent swarm.

Now all Europe is in turmoil. The French war-cloud casts its ominous

shadow everywhere. Even in England mutterings of the French Revolution

are not without an echo. The spirit of war is in the air. And yet, as

before, the spirit of science also is in the air. The strain of the

political relations does not prevent a perpetual exchange of courtesy

between scientific men and scientific bodies of various nations. Davy's

dictum that "science knows no country" is perpetually exemplified in

practice. And at the Royal Society, to match the great figures that were

upon the scene a century before, there are such men as the eccentric

Cavendish, the profound Wollaston, the marvellously versatile Priestley,

and the equally versatile and even keener-visioned Rumford. Here, too,

are Herschel, who is giving the world a marvellous insight into the

constitution of the universe; and Hutton, who for the first time gains a

clear view of the architecture of our earth's crust; and Jenner, who is

rescuing his fellow-men from the clutches of the most deadly of plagues;

to say nothing of such titanic striplings as Young and Davy, who are

just entering the scientific lists. With such a company about us we are

surely justified in feeling that the glory of England as a scientific

centre has not dimmed in these first hundred and thirty years of the

Royal Society's existence.

And now, as we view the radiometer, the scene shifts by yet another

century, and we come out of cloud-land and into our own proper age. We

are at the close of the nineteenth century--no, I forget, we are fairly

entering upon the twentieth. Need I say that these again are troublous

times? Man still wages warfare on his fellow-man as he has done time

out of mind; as he will do--who shall say how long? But meantime, as

of yore, the men of science have kept steadily on their course. But

recently here at the Royal Society were seen the familiar figures of

Darwin and Lyell and Huxley and Tyndall. Nor need we shun any comparison

with the past while the present lists can show such names as Wallace,

Kelvin, Lister, Crookes, Foster, Evans, Rayleigh, Ramsay, and Lock-yer.

What revolutionary advances these names connote! How little did those

great men of the closing decades of the seventeenth and eighteenth

centuries know of the momentous truths of organic evolution for which

the names of Darwin and Wallace and Huxley stand! How little did

they know a century ago, despite Hutton's clear prevision, of these

marvellous slow revolutions through which, as Lyell taught us, the

earth's crust had been built up! Not even Jen-ner could foresee a

century ago the revolution in surgery which has been effected in our

generation through the teachings of Lister.

And what did Rumford and Davy know of energy in its various

manifestations as compared with the knowledge of to-day, of Crookes

and Rayleigh and Ramsay and Kelvin? What would Joseph Priestley, the

discoverer of oxygen, and Cavendish, the discoverer of nitrogen,

think could they step into the laboratory of Professor Ramsay and see

test-tubes containing argon and helium and krypton and neon and zenon?

Could they more than vaguely understand the papers contributed in recent

years to the Royal Society, in which Professor Ramsay explains how these

new constituents of the atmosphere are obtained by experiments on liquid

air. "Here," says Professor Ramsay, in effect, in a late paper to the

society, "is the apparatus with which we liquefy hydrogen in order to

separate neon from helium by liquefying the former while the helium

still remains gaseous." Neon, helium, liquid air, liquid hydrogen--these

would seem strange terms to the men who on discovering oxygen and

nitrogen named them "dephlogisticated air" and "phlogisti-cated air"

respectively.

Again, how elementary seems the teaching of Her-schel, wonderful though

it was in its day, when compared with our present knowledge of the

sidereal system as outlined in the theories of Sir Norman Lock-yer.

Herschel studied the sun-spots, for example, with assiduity, and even

suggested a possible connection between sun-spots and terrestrial

weather. So far, then, he would not be surprised on hearing the

announcement of Professor Lockyer's recent paper before the Royal

Society on the connection between sun-spots and the rainfall in India.

But when the paper goes on to speak of the actual chemical nature of the

sun-spots, as tested by a spectroscope; to tell of a "cool" stage when

the vapor of iron furnishes chief spectrum lines, and of a "hot" stage

when the iron has presumably been dissociated into unknown "proto-iron"

constituents--then indeed does it go far beyond the comprehension of the

keenest eighteenth-century intellect, though keeping within the range of

understanding of the mere scientific tyro of to-day.

Or yet again, consider a recent paper contributed by Professor Lockyer

to the Royal Society, entitled "The New Star in Perseus: Preliminary

Note"--referring to the new star that flashed suddenly on the vision of

the terrestrial observers at more than first magnitude on February 22,

1901. This "star," the paper tells us, when studied by its spectrum,

is seen to be due to the impact of two swarms of meteors out in

space--swarms moving in different directions "with a differential

velocity of something like seven hundred miles a second." Every

astronomer of to-day understands how such a record is read from the

displacement of lines on the spectrum, as recorded on the photographic

negative. But imagine Sir William Herschel, roused from a century's

slumber, listening to this paper, which involves a subject of which he

was the first great master. "Ebulae," he might say; "yes, they were a

specialty of mine; but swarms of meteors--I know nothing of these. And

'spectroscopes,' 'photographs'--what, pray, are these? In my day there

were no such words or things as spectroscope and photograph; to my mind

these words convey no meaning."

But why go farther? These imaginings suffice to point a moral that he

who runs may read. Of a truth the march of science still goes on as it

has gone on with steady tread throughout the long generations of the

Royal Society's existence. If the society had giants among its members

in the days of its childhood and adolescence, no less are there giants

still to keep up its fame in the time of its maturity. The place of

England among the scientific constellations is secure through tradition,

but not through tradition alone.

III. THE ROYAL INSTITUTION AND THE LOW-TEMPERATURE RESEARCHES

FOUNDATION AND FOUNDER

"GEORGE THE THIRD, by the Grace of God King of Great Britain, France,

and Ireland, Defender of the Faith, etc., to all to whom these presents

shall come, greeting. Whereas several of our loving subjects are

desirous of forming a Public Institution for diffusing the knowledge and

facilitating the general introduction of Useful Mechanical Inventions

and Improvements; and for teaching, by Courses of Philosophical Lectures

and Experiments, the Application of Science to the Common Purposes of

Life, we do hereby give and grant"--multifarious things which need not

here be quoted. Such are the opening words of the charter with which, a

little more than a century ago, the Royal Institution of Great Britain

came into existence and received its legal christening. If one reads on

he finds that the things thus graciously "given and granted," despite

all the official verbiage, amount to nothing more than royal sanction

and approval, but doubtless that meant more in the way of assuring

popular approval than might at first glimpse appear. So, too, of the

list of earls, baronets, and the like, who appear as officers and

managers of the undertaking, and who are described in the charter as

"our right trusty and right well-beloved cousins," "our right trusty

and well-beloved counsellors," and so on, in the skilfully graduated

language of diplomacy. The institution that had the King for patron and

such notables for officers seemed assured a bright career from the very

beginning. In name and in personnel it had the flavor of aristocracy,

a flavor that never palls on British palate. And right well the

institution has fulfilled its promise, though in a far different way

from what its originator and founder anticipated.

Its originator and founder, I say, and say advisedly; for, of course,

here, as always, there is one man who is the true heart and soul of the

movement, one name that stands, in truth, for the whole project, and to

which all the other names are mere appendages. You would never suspect

which name it is, in the present case, from a study of the charter,

for it appears well down the file of graded titles, after "cousins" and

"counsellors" have had their day, and is noted simply as "our trusty

and well-beloved Benjamin, Count of Rumford, of the Holy Roman Empire."

Little as there is to signalize it in the charter, this is the name of

the sole projector of the enterprise in its incipiency, of the

projector of every detail, of the writer of the charter itself even. The

establishment thus launched with royal title might with full propriety

have been called, as indeed it sometimes is called, the Rumford

Institution.

The man who thus became the founder of this remarkable institution was

in many ways a most extraordinary person. He was an American by birth,

and if not the most remarkable of Americans, he surely was destined to

a more picturesque career than ever fell to the lot of any of his

countrymen of like eminence. Born on a Massachusetts farm, he was a

typical "down-east Yankee," with genius added to the usual shrewd,

inquiring mind and native resourcefulness. He was self-educated and

self-made in the fullest sense in which those terms can be applied. At

fourteen he was an unschooled grocer-lad--Benjamin Thompson by name--in

a little New England village; at forty he was a world-famous savant,

as facile with French, Italian, Spanish, and German as with his native

tongue; he had become vice-president and medallist of the Royal

Society, member of the Berlin National Academy of Science, of the French

Institute, of the American Academy of Science, and I know not what other

learned bodies; he had been knighted in Great Britain after serving

there as under-secretary of state and as an officer; and he had risen

in Bavaria to be more than half a king in power, with the titles, among

others, of privy councillor of state, and head of the war department,

lieutenant-general of the Bavarian armies, holder of the Polish order of

St. Stanislas and the Bavarian order of the White Eagle, ambassador to

England and to France, and, finally, count of the Holy Roman Empire.

Once, in a time of crisis, Rumford was actually left at the head of

a council of regency, in full charge of Bavarian affairs, the elector

having fled. The Yankee grocer-boy had become more than half a king.

Never, perhaps, did a man of equal scientific attainments enjoy a

corresponding political power. Never was political power wielded more

justly by any man.

For in the midst of all his political and military triumphs, Rumford

remained at heart to the very end the scientist and humanitarian. He

wielded power for the good of mankind; he was not merely a ruler but

a public educator. He taught the people of Bavaria economy and Yankee

thrift. He established kitchens for feeding the poor on a plan that was

adopted all over Europe; but, better yet, he created also workshops for

their employment and pleasure-gardens for their recreation. He actually

banished beggary from the principality.

It was in the hope of doing in some measure for London what he had done

for Munich that this large-brained and large-hearted man was led to the

project of the Royal Institution. He first discussed his plans with a

committee of the Society for Alleviating the Condition of the Poor, for

it was the poor, the lower ranks of society, whom he wished chiefly to

benefit. But he knew that to accomplish his object, he must work through

the aristocratic channels; hence the name of the establishment and the

charter with its list of notables. The word institution was selected

by Rumford, after much deliberation, as, on the whole, the least

objectionable title for the establishment, as having a general

inclusiveness not possessed by such words as school or college. Yet in

effect it was a school which Rumford intended to found--a school for

the general diffusion of useful knowledge. There were to be classes

for mechanics, and workshops, kitchens, and model-rooms, where the

"application of science to the useful purposes of life" might be

directly and practically taught; also a laboratory for more technical

investigations, with a "professor" in charge, who should also deliver

popular lectures on science. Finally, there was to be a scientific

library.

All these aims were put into effect almost from the beginning. The

necessary funds were supplied solely by popular subscription and by the

sale of lecture tickets (as all funds of the institution have been ever

since), and before the close of the year 1800 Rumford's dream had become

an actuality--as this practical man's dreams nearly always did. The new

machine did not move altogether without friction, of course, but on the

whole all went well for the first few years. The institution had found

a local habitation in a large building in Albemarle Street, the same

building which it still occupies, and for a time Rumford lived there and

gave the enterprise his undivided attention. He appointed the brilliant

young Humphry Davy to the professorship of chemistry, and the even

more wonderful Thomas Young to that of natural philosophy. He saw the

workshops and kitchens and model-rooms in running order--the entire

enterprise fully launched. Then other affairs, particularly an

attachment for a French lady, the widow of the famous chemist Lavoisier

(whom he subsequently married, to his sorrow), called him away from

England never to return. And the first chapter in the history of the

Royal Institution was finished.

METHOD AND RESULT

Rumford, the humanitarian, gone, a curious change came over the spirit

of the enterprise he had founded. The aristocrats who at first were

merely ballast for the enterprise now made their influence felt. With

true British reserve, they announced their belief that the education of

the masses involved a dangerous political tendency. Hence the mechanics'

school was suspended and the workshops and kitchens abolished; in

a word, the chief ends for which the institution was founded were

annulled. The library and the lectures remained, to be sure, but they

were for the amusement of the rich, not for the betterment of the poor.

It was the West End that made a fad of the institution and a society

function of the lectures of Sydney Smith and of the charming youth Davy.

Thus the institution came to justify its aristocratic title and its

regal patronage; and the poor seemed quite forgotten.

But indeed the institution itself was poor enough in these days, after

the first flush of enthusiasm died away, and it is but fair to remember

that without the support of its popular lectures its very existence

would have been threatened. Nor in any event are regrets much in order

over the possible might-have-beens of an institution whose laboratories

were the seat of the physical investigations of Thomas Young, through

which the wave theory of light first gained a footing, and of the

brilliant chemical researches of Davy, which practically founded the

science of electro-chemistry and gave the chemical world first knowledge

of a galaxy of hitherto unknown elements. Through the labors of

these men, and through the popular lecture-courses delivered at the

institution by such other notables of science as Wollaston, Dalton, and

Rum-ford, the enterprise had become world-famous before the close of the

first decade of its existence.

From that day till this the character of the Royal Institution has

not greatly changed. The enterprise shifted around during its earliest

years, while it was gaining its place in the scheme of things; but once

that was found, like a true British institution it held its course with

an inertia that a mere century of time could not be expected to alter.

Rumford was the sole founder of the enterprise, but it was Davy who

gave it the final and definitive cast. He it was who established the

tradition that the Royal Institution was to be essentially a laboratory

for brilliant original investigations, the investigator to deliver

a yearly course of lectures, but to be otherwise untrammelled. It

occupied, and has continued to occupy, the anomalous position of a

school to which pupils are on no account admitted, and whose professors

teach nothing except by a brief course of lectures to which whoever

cares to pay the admission price may freely enter.

But the marvellous results achieved at the Royal Institution have more

than justified the existence of so anomalous an enterprise. Superlatives

are always dangerous, but it may well be doubted whether there is

another single institution in the world where so many novel original

discoveries in physical science have been made as have been brought to

light in the laboratories of the building on Albemarle Street during

this first century of its occupancy; for practically all that is to

be credited to Thomas Young, Humphry Davy, Michael Faraday, and John

Tyndall, not to mention living investigators, is to be credited also to

the Royal Institution, whose professorial chairs these great men have

successively occupied. Davy spent here the best years of his youth

and prime. Faraday, his direct successor, came to the institution in a

subordinate capacity as a mere boy, and was the life of the institution

for half a century. Tyndall gave it forty years of service. What wonder,

then, that the Briton speaks of the institution as the "Pantheon of

Science"?

If you visit the Royal Institution to-day you will find it in most

exterior respects not unlike what it presumably was a century ago. Its

long, stone front, dinged with age, with its somewhat Pantheon-like

colonnade, has an appearance of dignity rather than of striking

impressiveness. The main entrance, jutting full on the sidewalk, is at

the street level, and the glass door gives hospitable glimpses of the

interior. Entering, one finds himself in a main central hall, at the

foot of the main central staircase. The air of eminent respectability

so characteristic of the British institution is over all; likewise

the pervasive hush of British reserve. But you will not miss also the

atmosphere of sincere if uneffusive British courtesy.

At your right, as you mount the stairway, is a large statue of Faraday;

on the wall right ahead is a bronze medallion of Tyndall, placed beneath

a large portrait of Davy. At the turn of the stairs is a marble bust of

Wollaston. Farther on, in hall and library, you will find other busts of

Faraday, other portraits of Davy; portraits of Faraday everywhere,

and various other busts of notables who have had connection with the

institution. You will be shown the lecture-hall where Davy, Faraday,

and Tyndall pronounced their marvellous discourses; the arrangement, the

seats, the cushions even if appearances speak truly, and certainly the

lecture-desk itself, unchanged within the century. You may see the crude

balance, clumsy indeed to modern eyes, with which Davy performed his

wonders. The names and the memories of three great men--Davy,

Faraday, and Tyndall--will be incessantly before you, and the least

impressionable person could not well escape a certain sense of

consecration of his surroundings. The hush that is over everything seems

but fitting.

All that is as it should be. But there are other memories connected with

these surroundings which are not so tangibly presented to the senses.

For where, amid all these busts and portraits, is the image of that

other great man, the founder of the institution, the sole originator

of the enterprise which has made possible the aggregation of all

these names and these memories? Where are the remembrances of

that extraordinary man whom the original charter describes as "our

well-beloved Benjamin, Count of Rumford?" Well, you will find a portrait

of him, it is true, if you search far enough, hung high above a doorway

in a room with other portraits. But one finds it hard to escape the

feeling that there has been just a trifling miscarriage of justice in

the disposal. Doubtless there was no such intention, but the truth seems

to be that the glamour of the newer fame of Faraday has dazzled a little

the eyes of the rulers of the institution of the present generation.

But that, after all, is a small matter about which to quibble. There is

glory enough for all in the Royal Institution, and the disposal of busts

and portraits is unworthy to be mentioned in connection with the lasting

fame of the great men who are here in question. It would matter little

if there were no portrait at all of Rumford here, for all the world

knows that the Royal Institution itself is in effect his monument. His

name will always be linked in scientific annals with the names of Young,

Davy, Faraday, and Tyndall. And it is worthy such association, for

neither in native genius nor in realized accomplishments was Rumford

inferior to these successors.

FROM LIQUID CHLORINE TO LIQUID HYDROGEN

Nor is it merely by mutual association with the history of the Royal

Institution that these great names are linked. There was a curious

and even more lasting bond between them in the character of their

scientific discoveries. They were all pioneers in the study of those

manifestations of molecular activity which we now, following Young

himself, term energy. Thus Rumford, Davy, and Young stood almost alone

among the prominent scientists of the world at the beginning of the

century in upholding the idea that heat is not a material substance--a

chemical element--but merely a manifestation of the activities of

particles of matter. Rumford's papers on this thesis, communicated to

the Royal Society, were almost the first widely heralded claims for this

then novel idea. Then Davy came forward in support of Rumford, with

his famous experiment of melting ice by friction. It was perhaps

this intellectual affinity that led Rumford to select Davy for

the professorship at the Royal Institution, and thus in a sense to

predetermine the character of the scientific work that should be

accomplished there--the impulse which Davy himself received from

Rum-ford being passed on to his pupil Faraday. There is, then, an

intangible but none the less potent web of association between the

scientific work of Rumford and some of the most important researches

that were conducted at the Royal Institution long years after his death;

and one is led to feel that it was not merely a coincidence that some

of Faraday's most important labors should have served to place on a firm

footing the thesis for which Rumford battled; and that Tyndall should

have been the first in his "beautiful book" called _Heat, a Mode of

Motion_, to give wide popular announcement to the fact that at last the

scientific world had accepted the proposition which Rumford had vainly

demonstrated three-quarters of a century before.

This same web of association extends just as clearly to the most

important work which has been done at the Royal Institution in the

present generation, and which is still being prosecuted there--the

work, namely, of Professor James Dewar on the properties of matter at

excessively low temperatures. Indeed, this work is in the clearest sense

a direct continuation of researches which Davy and Faraday inaugurated

in 1823 and which Faraday continued in 1844. In the former year Faraday,

acting on a suggestion of Davy's, performed an experiment which resulted

in the production of a "clear yellow oil" which was presently proved to

be liquid chlorine. Now chlorine, in its pure state, had previously been

known (except in a forgotten experiment of Northmore's) only as a gas.

Its transmutation into liquid form was therefore regarded as a very

startling phenomenon. But the clew thus gained, other gases were

subjected to similar conditions by Davy, and particularly by Faraday,

with the result that several of them, including sulphurous, carbonic,

and hydrochloric acids were liquefied. The method employed, stated in

familiar terms, was the application of cold and of pressure. The results

went far towards justifying an extraordinary prediction made by that

extraordinary man, John Dalton, as long ago as 1801, to the effect that

by sufficient cooling and compressing all gases might be transformed

into liquids--a conclusion to which Dalton had vaulted, with the

sureness of supreme genius, from his famous studies of the properties of

aqueous vapor.

Between Dalton's theoretical conclusion, however, and experimental

demonstration there was a tremendous gap, which the means at the

disposal of the scientific world in 1823 did not enable Davy and Faraday

more than partially to bridge. A long list of gases, including the

familiar oxygen, hydrogen, and nitrogen, resisted all their efforts

utterly--notwithstanding the facility with which hydrogen and oxygen

are liquefied when combined in the form of water-vapor, and the relative

ease with which nitrogen and hydrogen, combined to form ammonia, could

also be liquefied. Davy and Faraday were well satisfied of the truth of

Dalton's proposition, but they saw the futility of further efforts

to put it into effect until new means of producing, on the one hand,

greater pressures, and, on the other, more extreme degrees of cold,

should be practically available. So the experiments of 1823 were

abandoned.

But in 1844 Faraday returned to them, armed now with new weapons, in the

way of better air-pumps and colder freezing mixtures, which the labors

of other workers, chiefly Thilorier, Mitchell, and Natterer, had made

available. With these new means, and without the application of any

principle other than the use of cold and pressure as before, Faraday now

succeeded in reducing to the liquid form all the gases then known with

the exception of six; while a large number of these substances were

still further reduced, by the application of the extreme degrees of

cold now attained, to the condition of solids. The six gases which still

proved intractable, and which hence came to be spoken of as "permanent

gases," were nitrous oxide, marsh gas, carbonic oxide, oxygen, nitrogen,

and hydrogen.

These six refractory gases now became a target for the experiments of a

host of workers in all parts of the world. The resources of mechanical

ingenuity of the time were exhausted in the effort to produce low

temperatures on the one hand and high pressures on the other. Thus

Andrews, in England, using the bath of solid carbonic acid and ether

which Thilorier had discovered, and which produces a degree of cold

of--80° Centigrade, applied a pressure of five hundred atmospheres, or

nearly four tons to the square inch, without producing any change of

state. Natterer increased this pressure to two thousand seven hundred

atmospheres, or twenty-one tons to the square inch, with the same

negative results. The result of Andrews' experiments in particular was

the final proof of what Cagniard de la Tour had early suspected

and Faraday had firmly believed, that pressure alone, regardless of

temperature, is not sufficient to reduce a gas to the liquid state. In

other words, the fact of a so-called "critical temperature," varying

for different substances, above which a given substance is always a gas,

regardless of pressure, was definitively discovered. It became clear,

then, that before the resistant gases would be liquefied means of

reaching extremely low temperatures must be discovered. And for this,

what was needed was not so much new principles as elaborate and

costly machinery for the application of a principle long familiar--the

principle, namely, that an evaporating liquid reduces the temperature of

its immediate surroundings, including its own substance.

Ingenious means of applying this principle, in connection with the means

previously employed, were developed independently by Pictet in Geneva

and Cailletet in Paris, and a little later by the Cracow professors

Wroblewski and Olzewski, also working independently. Pictet, working on

a commercial scale, employed a series of liquefied gases to gain lower

and lower temperatures by successive stages. Evaporating sulphurous acid

liquefied carbonic acid, and this in evaporating brought oxygen under

pressure to near its liquefaction point; and, the pressure being

suddenly released (a method employed in Faraday's earliest experiments),

the rapid expansion of the compressed oxygen liquefies a portion of

its substance. This result was obtained in 1877 by Pictet and Cailletet

almost simultaneously. Cailletet had also liquefied the newly discovered

acetylene gas. Five years later Wroblewski liquefied marsh gas, and the

following year nitrogen; while carbonic oxide and nitrous oxide yielded

to Olzewski in 1884. Thus forty years of effort had been required to

conquer five of Faraday's refractory gases, and the sixth, hydrogen,

still remains resistant. Hydrogen had, indeed, been seen to assume the

form of visible vapor, but it had not been reduced to the so-called

static state--that is, the droplets had not been collected in an

appreciable quantity, as water is collected in a cup. Until this should

be done, the final problem of the liquefaction of hydrogen could not be

regarded as satisfactorily solved.

More than another decade was required to make this final step in the

completion, of Faraday's work. And, oddly enough, yet very fittingly,

it was reserved for Faraday's successor in the chair at the Royal

Institution to effect this culmination. Since 1884 Professor Dewar's

work has made the Royal Institution again the centre of low-temperature

research. By means of improved machinery and of ingenious devices for

shielding the substance operated on from the accession of heat, to which

reference will be made more in detail presently, Professor Dewar was

able to liquefy the gas fluorine, recently isolated by Moussan, and the

recently discovered gas helium in 1897. And in May, 1898, he was able to

announce that hydrogen also had yielded, and for the first time in

the history of science that* elusive substance, hitherto "permanently"

gaseous, was held as a tangible liquid in a cuplike receptacle; and this

closing scene of the long struggle was enacted in the same laboratory in

which Faraday performed the first liquefaction experiment with chlorine

just three-quarters of a century before.

It must be noted, however, that this final stage in the liquefaction

struggle was not effected through the use of the principle of

evaporating liquids which has just been referred to, but by the

application of a quite different principle and its elaboration into a

perfectly novel method. This principle is the one established long ago

by Joule and Thomson (Lord Kelvin), that compressed gases when allowed

to expand freely are lowered in temperature. In this well-known

principle the means was at hand greatly to simplify and improve the

method of liquefaction of gases, only for a long time no one recognized

the fact. Finally, however, the idea had occurred to two men almost

simultaneously and quite independently. One of these was Professor

Linde, the well-known German experimenter with refrigeration processes;

the other, Dr. William Hampson, a young English physician. Each of these

men conceived the idea--and ultimately elaborated it in practice--of

accumulating the cooling effect of an expanding gas by allowing the

expansion to take place through a small orifice into a chamber in which

the coil containing the compressed gas was held. In Dr. Hampson's words:

"The method consists in directing all the gas immediately after its

expansion over the coils which contain the compressed gas that is on its

way to the expansion-point. The cold developed by expansion in the first

expanded gas is thus communicated to the oncoming compressed gas, which

consequently expands from, and therefore to, a lower temperature

than the preceding portion. It communicates in the same way its own

intensified cold to the succeeding portion of compressed gas, which, in

its turn, is made colder, both before and after expansion, than any

that had gone before. This intensification of cooling goes on until the

expansion-temperature is far lower than it was at starting; and if

the apparatus be well arranged the effect is so powerful that even the

smaller amount of cooling due to the free expansion of gas through a

throttle-valve, though pronounced by Siemens and Coleman incapable

of being utilized, may be made to liquefy air without using other

refrigerants."

So well is this principle carried out in Dr. Hamp-son's apparatus for

liquefying air that compressed air passing into the coil at ordinary

temperature without other means of refrigeration begins to liquefy in

about six minutes--a result that seems almost miraculous when it is

understood that the essential mechanism by which this is brought about

is contained in a cylinder only eighteen inches long and seven inches in

diameter.

As has been said, it was by adopting this principle of self-intensive

refrigeration that Professor Dewar was able to liquefy hydrogen. More

recently the same result has been attained through use of the same

principle by Professor Ramsay and Dr. Travers at University College,

London, who are to be credited also with first publishing a detailed

account of the various stages of the process. It appears that the use of

the self-intensification principle alone is not sufficient with hydrogen

as it is with the less volatile gases, including air, for the reason

that at all ordinary temperatures hydrogen does not cool in expanding,

but actually becomes warmer. It is only after the compressed hydrogen

has been cooled by immersion in refrigerating media of very low

temperature that this gas becomes amenable to the law of cooling on

expansion. In the apparatus used at University College the coil of

compressed hydrogen is passed successively through (1) a jar containing

alcohol and solid carbonic acid at a temperature of--80° Centigrade; (2)

a chamber containing liquid air at atmospheric pressure, and (3)

liquid air boiling in a vacuum bringing the temperature to perhaps 2050

Centigrade before entering the Hampson coil, in which expansion and

the self-intensive refrigeration lead to actual liquefaction. With this

apparatus Dr. Travers succeeded in producing an abundant quantity of

liquid hydrogen for use in the experiments on the new gases that were

first discovered in the same laboratory through the experiments on

liquid air--gases about which I shall have something more to say in

another chapter.

PRINCIPLES AND EXPERIMENTS

At first blush it seems a very marvellous thing, this liquefaction

of substances that under all ordinary conditions are gaseous. It is

certainly a little startling to have a cup of clear, water-like liquid

offered one, with the assurance that it is nothing but air; still more

so to have the same air presented in the form of a white "avalanche

snow." In a certain sense it is marvellous, because the mechanical

difficulties that have been overcome in reducing the air to these

unusual conditions are great. Yet, in another and broader view, there

is nothing more wonderful about liquid air than about liquid water, or

liquid mercury, or liquid iron. Long before air was actually liquefied,

it was perfectly understood by men of science that under certain

conditions it could be liquefied just as surely as water, mercury, iron,

and every other substance could be brought to a similar state. This

being known, and the principles involved understood, had there been

nothing more involved than the bare effort to realize these conditions

all the recent low-temperature work would have been mere scientific

child's-play, and liquid air would be but a toy of science. But in point

of fact there are many other things than this involved; new principles

were being searched for and found in the course of the application of

the old ones; new light was being thrown into many dark corners; new

fields of research, some of them as yet barely entered, were being

thrown open to the investigator; new applications of energy, of vast

importance not merely in pure science but in commercial life as well,

were being made available. That is why the low-temperature work must be

regarded as one of the most important scientific accomplishments of our

century.

At the very outset it was this work in large measure which gave the

final answer to the long-mooted question as to the nature of heat,

demonstrating the correctness of Count Rumford's view that heat is

only a condition not itself a substance. Since about the middle of the

century this view, known as the mechanical theory of heat, has been the

constant guide of the physicists in all their experiments, and any

one who would understand the low-temperature phenomena must keep this

conception of the nature of heat clearly and constantly in mind. To

understand the theory, one must think of all matter as composed

of minute isolated particles or molecules, which are always in

motion--vibrating, if you will. He must mentally magnify and

visualize these particles till he sees them quivering before him,

like tuning-forks held in the hand. Remember, then, that, like the

tuning-fork, each molecule would, if left to itself, quiver less and

less violently, until it ran down altogether, but that the motion thus

lessening is not really lost. It is sent out in the form of ether waves,

which can set up like motion in any other particles which they reach, be

they near or remote; or it is transmitted as a direct push--a kick,

if you will--to any other particle with which the molecule comes in

physical contact.

But note now, further, that our molecule, while incessantly giving out

its energy of motion in ether waves and in direct pushes, is at the same

time just as ceaslessly receiving motion from the ether waves made by

other atoms, and by the return push of the molecules against which it

pushes. In a word, then, every molecule of matter is at once a centre

for the distribution of motion (sending out impulses which affect,

sooner or later, every other atom of matter in the universe), and, from

the other point of view, also a centre for the reception of motion from

every direction and from every other particle of matter in the universe.

Whether any given molecule will on the whole gain motion or lose it

depends clearly on the simple mechanical principles of give and take.

From equally familiar mechanical principles, it is clear that our

vibrating molecule, in virtue of its vibrations, is elastic, tending to

be thrown back from every other molecule with which it comes in contact,

just as a vibrating tuning-fork kicks itself away from anything it

touches. And of course the vigor of the recoil will depend upon the

vigor of the vibration and the previous movements. But since these

movements constitute temperature, this is another way of saying that

the higher the temperature of a body the more its molecules will tend to

spring asunder, such separation in the aggregate constituting expansion

of the mass as a whole. Thus the familiar fact of expansion of a body

under increased temperature is explained.

But now, since all molecules are vibrating, and so tending to separate,

it is clear that no unconfined mass of molecules would long remain in

contiguity unless some counter influence tended to draw them together.

Such a counter influence in fact exists, and is termed the "force" of

cohesion. This force is a veritable gravitation influence, drawing every

molecule towards every other molecule. Possibly it is identical with

gravitation. It seems subject to some law of decreasing in power with

the square of the distance; or, at any rate, it clearly becomes less

potent as the distance through which it operates increases.

Now, between this force of cohesion which tends to draw the molecules

together, and the heat vibrations which tend to throw the molecules

farther asunder, there seems to be an incessant battle. If cohesion

prevails, the molecules are held for the time into à relatively fixed

system, which we term the solid state. If the two forces about balance

each other, the molecules move among themselves more freely but maintain

an average distance, and we term the condition the liquid state. But if

the heat impulse preponderates, the molecules (unless restrained from

without) fly farther and farther asunder, moving so actively that when

they collide the recoil is too great to be checked by cohesion, and this

condition we term the gaseous state.

Now after this statement, it is clear that what the low-temperature

worker does when he would liquefy a gas is to become the champion of the

force of cohesion. He cannot directly aid it, for so far as is known it

is an unalterable quantity, like gravitation. But he can accomplish the

same thing indirectly by weakening the power of the rival force. Thus,

if he encloses a portion of gas in a cylinder and drives a piston down

against it, he is virtually aiding cohesion by forcing the molecules

closer together, so that the hold of cohesion, acting through a less

distance, is stronger. What he accomplishes here is not all gain,

however, for the bounding molecules, thus jammed together, come in

collision with one another more and more frequently, and thus their

average activity of vibration is increased and not diminished; in

other words, the temperature of the gas has risen in virtue of the

compression. Compression alone, then, will not avail to enable cohesion

to win the battle.

But the physicist has another resource. He may place the cylinder of gas

in a cold medium, so that the heat vibrations sent into it will be less

vigorous than those it sends out. That is a blow the molecule cannot

withstand. It is quite impotent to cease sending out the impulses

however little comes in return; hence the aggregate motion becomes less

and less active, until finally the molecule is moving so sluggishly

that when it collides with its fellow cohesion is able to hold it there.

Cohesion, then, has won the battle, and the gas has become a liquid.

Such, stated in terms of the mechanical theory of heat, is what is

brought to pass when a gas is liquefied in the laboratory of the

physicist. It remains only to note that different chemical substances

show the widest diversity as to the exact point of temperature at which

this balance of the expansive and cohesive tendencies is affected, but

that the point, under uniform conditions of pressure, is always the same

for the same substance. This diversity has to do pretty clearly with the

size of the individual molecules involved; but its exact explanation is

not yet forthcoming, and, except in a general way, the physicist

would not be able to predict the "critical temperature" of any new gas

presented to him. But once this has been determined by experiment, he

always knows just what to expect of any given substance. He knows, for

example, that in a mixture of gases hydrogen would still remain gaseous

after all the others had assumed the liquid state, and most of them the

solid state as well.

These mechanical conceptions well in mind, it is clear that what the

would-be liquefier of gases has all along sought to attain is merely

the insulation of the portion of matter with which he worked against the

access of heat-impulse from its environment. It is clear that were any

texture known which would permit a heat-impulse to pass through it in

one direction only, nothing more would be necessary than to place a

portion of gas in such a receptacle of this substance, so faced as to

permit egress but not entrance of the heat, and the gas thus enclosed,

were it hydrogen itself, would very soon become liquid and solid,

through spontaneous giving off of its energy, without any manipulation

whatever. Contrariwise, were the faces of the receptacle reversed, a

piece of iron placed within it would be made red-hot and melted though

the receptacle were kept packed in salt and ice and no heat applied

except such as came from this freezing mixture. One could cook a

beefsteak with a cake of ice had he but such a material as this with

which to make his stove. Not even Rumford or our modern Edward Atkinson

ever dreamed of such economy of fuel as that.

But, unfortunately, no such substance as this is known, nor, indeed, any

substance that will fully prevent the passage of heat-impulses in either

direction. Hence one of the greatest tasks of the experimenters has

been to find a receptacle that would insulate a cooled substance even

partially from the incessant bombardment of heat-impulses from without.

It is obvious that unless such an insulating receptacle could be

provided none of the more resistent gases, such as oxygen, could be

long kept liquid, even when once brought to that condition, since an

environment of requisite frigidity could not practicably be provided.

But now another phase of the problem presents itself to the

experimenter. Oxygen has assumed the quiescent liquid state, to be

sure, but in so doing it has fallen below the temperature of its cooling

medium; hence it is now receiving from that medium more energy of

vibration than it gives, and unless this is prevented very soon its

particles will again have power to kick themselves apart and resume the

gaseous state. Something, then, must be done to insulate the liquefied

gas, else it will retain the liquid state for too short a time to be

much experimented with. How might such insulation be accomplished?

The most successful attack upon this important problem has been made by

Professor Dewar. He invented a receptacle for holding liquefied gases

which, while not fulfilling the ideal conditions referred to above, yet

accomplishes a very remarkable degree of heat insulation. In consists of

a glass vessel with double walls, the space between which is rendered

a vacuum of the highest practicable degree. This vacuum, containing

practically no particles of matter, cannot, of course, convey

heat-impulses to or from the matter in the receptacle with any degree

of rapidity. Thus one of the two possible means of heat transfer is shut

off and a degree of insulation afforded the liquefied substance. But

of course the other channel, ether radiation, remains. Even this may be

blocked to a large extent, however, by leaving a trace of mercury vapor

in the vacuum space, which will be deposited as a fine mirror on

the inner surface of the chamber. This mirror serves as an admirable

reflector of the heat-rays that traverse the vacuum, sending more

than half of them back again. So, by the combined action of vacuum and

mirror, the amount of heat that can penetrate to the interior of the

receptacle is reduced to about one-thirtieth of what would enter an

ordinary vessel. In other words, a quantity of liquefied gas which would

evaporate in one minute from an ordinary vessel will last half an hour

in one of Professor Dewar's best vacuum vessels. Thus in one of these

vessels a quantity of liquefied air, for example, can be kept for a

considerable time in an atmosphere at ordinary temperature, and will

only volatilize at the surface, like water under the same conditions,

though of course more rapidly; whereas the same liquid in an ordinary

vessel would boil briskly away, like water over a fire. Only, be it

remembered, the air in "boiling" is at a temperature of about one

hundred and eighty degrees below zero, so that it would instantly freeze

almost any substance placed into it. A portion of alcohol poured on its

surface will be changed quickly into a globule of ice, which will

rattle about the sides of the vessel like a marble. That is not what one

ordinarily thinks of as a "boiling" temperature.

If the vacuum vessel containing a liquefied gas be kept in a cold

medium, and particularly if two vacuum tubes be placed together, so that

no exposed surface of liquid remains, a portion of liquefied air, for

example, may be kept almost indefinitely. Thus it becomes possible

to utilize the liquefied gas for experimental investigation of the

properties of matter at low temperatures that otherwise would be quite

impracticable. Great numbers of such experiments have been performed in

the past decade or so by all the workers with low temperatures already

mentioned, and by various others, including, fittingly enough, the

holder of the Rumford professorship of experimental physics at Harvard,

Professor Trowbridge. The work of Professor Dewar has perhaps been the

most comprehensive and varied, but the researches of Pictet, Wroblewski,

and Olzewski have also been important, and it is not always possible

to apportion credit for the various discoveries accurately, since

the authorities themselves are in unfortunate disagreement in several

questions of priority. But in any event, such questions of exact

priority have no great interest for any one but the persons directly

involved. We may quite disregard them here, confining attention to the

results themselves, which are full of interest.

The questions investigated have to do with the physical properties,

such as electrical conductivity, magnetic condition, light-absorption,

cohesion, and chemical affinities of matter at excessively low

temperatures. It is found that in all these regards most substances are

profoundly modified when excessively cooled. Thus if a piece of any pure

metal is placed in an electric circuit and plunged into liquid air, its

resistance to the passage of the electricity steadily decreases as the

metal cools, until at the temperature of the liquid it is very trifling

indeed. The conclusion seems to be justified that if the metal could be

still further cooled until it reached the theoretical "absolute zero,"

or absolutely heatless condition, the electrical resistance would also

be nil. So it appears that the heat vibrations of the molecules of a

pure metal interfere with the electrical current. The thought suggests

itself that this may be because the ether waves set up by the vibrating

molecules conflict with the ether strain which is regarded by some

theorists as constituting the electrical "current." But this simple

explanation falters before further experiments which show, paradoxically

enough, that the electrical resistance of carbon exactly reverses what

has just been said of pure metals, becoming greater and greater as the

carbon is cooled. If an hypothesis were invented to cover this case

there would still remain a puzzle in the fact that alloys of metals

do not act at all like the pure metals themselves, the electrical

resistance of such alloys being, for the most part, unaffected by

changed temperature. On the whole, then, the facts of electrical

conduction at low temperatures are quite beyond the reach of present

explanation. They must await a fuller knowledge of molecular conditions

in general than is at present available--a knowledge to which the

low-temperature work itself seems one of the surest channels.

Even further beyond the reach of present explanation are the facts as to

magnetic conditions at low temperatures. Even as to the facts themselves

different experimenters have differed somewhat, but the final conclusion

of Professor Dewar is that, after a period of fluctuation, the power of

a magnet repeatedly subjected to a liquid-air bath becomes permanently

increased. Various substances not markedly magnetic at ordinary

temperatures become so when cooled. Among these, as Professor Dewar

discovered, is liquid oxygen itself. Thus if a portion of liquid air be

further cooled until it assumes a semi-solid condition, the oxygen may

be drawn from the mass by a magnet, leaving a pure nitrogen jelly. These

facts are curious enough, and full of suggestion, but like all other

questions having to do with magnetism, they hold for the present

generation the double fascination of insoluble mystery. To be sure, one

may readily enough suggest that if magnetism be really a whirl in the

ether, this whirl is apparently interfered with by the waves of radiant

heat; or, again, that magnetism is presumably due to molecular motions

which are apparently interfered with by another kind of molecular

motions which we call heat vibrations; but there is a vagueness about

the terms of such guesses that leaves them clearly within the category

of explanations that do not explain.

When it comes to the phenomena of light, we can, as is fitting, see

our way a little more clearly, since, thanks to Thomas Young and his

successors, we know pretty definitely what light really is. So when

we learn that many substances change their color utterly at low

temperatures--red things becoming yellow and yellow things white,

for example--we can step easily and surely to at least a partial

explanation. We know that the color of any object depends simply

upon the particular ether waves of the spectrum which that particular

substance absorbs; and it does not seem anomalous that molecules packed

close together at--180° of temperature should treat the ether waves

differently than when relatively wide apart at an ordinary temperature.

Yet, after all, that may not be the clew to the explanation. The packing

of the molecules may have nothing to do with it. The real explanation

may lie in the change of the ether waves sent out by the vibrating

molecule; indeed, the fact that the waves of radiant heat and those of

light differ only in amplitude lends color to this latter supposition.

So the explanation of the changed color of the cooled substance is at

best a dubious one.

Another interesting light phenomenon is found in the observed fact that

very many substances become markedly phosphorescent at low temperatures.

Thus, according to Professor Dewar, "gelatine, celluloid, paraffine,

ivory, horn, and india-rubber become distinctly luminous, with a bluish

or greenish phosphorescence, after cooling to--180° and being stimulated

by the electric light." The same thing is true, in varying degrees,

of alcohol, nitric acid, glycerine, and of paper, leather, linen,

tortoise-shell, and sponge. Pure water is but slightly luminous, whereas

impure water glows brightly. On the other hand, alcohol loses its

phosphorescence when a trace of iodine is added to it. In general,

colored things are but little phosphorescent. Thus the white of egg is

very brilliant but the yolk much less so. Milk is much brighter than

water, and such objects as a white flower, a feather, and egg-shell

glow brilliantly. The most remarkable substances of all, says Professor

Dewar, whom I am all along quoting, are "the platinocyanides among

inorganic compounds and the ketonic compounds among organic. Ammonium

platinocyanide, cooled while stimulated by arc light, glows fully

at--180°; but on warming it glows like a lamp. It seems clear,"

Professor Dewar adds, "that the substance at this low temperature must

have acquired increased power of absorption, and it may be that at

the same time the factor of molecular friction or damping may have

diminished." The cautious terms in which this partial explanation is

couched suggest how far we still are from a full understanding of the

interesting phenomena of phosphorescence. That a molecule should be

able to vibrate in such a way as to produce the short waves of light,

dissevered from the usual linking with the vibrations represented by

high temperature, is one of the standing puzzles of physics. And the

demonstrated increase of this capacity at very low temperatures only

adds to the mystery.

There are at least two of the low-temperature phenomena, however,

that seem a little less puzzling--the facts, namely, that cohesion and

rigidity of structure are increased when a substance is cooled and that

chemical activity is very greatly reduced, in fact almost abolished.

This is quite what one would expect _a priori_--though no wise man would

dwell on his expectation in advance of the experiments--since the whole

question of liquids and solids _versus_ gases appears to be simply a

contest between cohesive forces that are tending to draw the molecules

together and the heat vibration which is tending to throw them apart.

As a substance changes from gas to liquid, and from liquid to solid,

contracting meantime, simply through the lessening of the heat

vibrations of its molecules, we might naturally expect that the solid

would become more and more tenacious in structure as its molecules came

closer and closer together, and at the same time became less and less

active, as happens when the solid is further cooled. And for once

experiment justifies the expectation. Professor De-war found that the

breaking stress of an iron wire is more than doubled when the wire

is cooled to the temperature of liquid air, and all other metals are

largely strengthened, though none other to quite the same degree.

He found that a spiral spring of fusible metal, which at ordinary

temperature was quickly drawn out into a straight wire by a weight

of one ounce, would, when cooled to -182 deg, support a weight of two

pounds, and would vibrate like a steel spring so long as it was cool.

A bell of fusible metal has a distinct metallic ring at this low

temperature; and balls of iron, tin, lead, or ivory cooled to -182

deg and dropped from a height, "in all cases have the rebound greatly

increased. The flattened surface of the lead is only one-third what it

would be at ordinary temperature." "These conditions are due solely to

the cooling, and persist only while the low temperature lasts."

If this increased strength and hardness of a contracted metal are

what one would expect on molecular principles, the decreased chemical

activity at low temperatures is no less natural-seeming, when one

reflects how generally chemical phenomena are facilitated by the

application of heat. In point of fact, it has been found that at the

temperature of liquid hydrogen practically all chemical activity

is abolished, the unruly fluorine making the only exception. The

explanation hinges on the fact that every atom, of any kind, has

power to unite with only a limited number of other atoms. When the

"affinities" of an atom are satisfied, no more atoms can enter into the

union unless some atoms already there be displaced. Such displacement

takes place constantly, under ordinary conditions of temperature,

because the vibrating atoms tend to throw themselves apart, and other

atoms may spring in to take the places just vacated--such interchange,

in fact, constituting the essence of chemical activity. But when the

temperature is reduced the heat-vibration becomes insufficient to

throw the atoms apart, hence any unions they chance to have made are

permanent, so long as the low temperature is maintained. Thus it is that

substances which attack one another eagerly at ordinary temperatures

will lie side by side, utterly inert, at the temperature of liquid air.

Under certain conditions, however, most interesting chemical experiments

have been made in which the liquefied gases, particularly oxygen, are

utilized. Thus Olzewski found that a bit of wood lighted and thrust into

liquid oxygen burns as it would in gaseous oxygen, and a red-hot iron

wire thrust into the liquid burns and spreads sparks of iron. But more

novel still was Dewar's experiment of inserting a small jet of ignited

hydrogen into the vessel of liquid oxygen; for the jet continued to

burn, forming water, of course, which was carried away as snow. The idea

of a gas-jet burning within a liquid, and having snow for smoke, is

not the least anomalous of the many strange conceptions that the

low-temperature work has made familiar.

PRACTICAL RESULTS AND ANTICIPATIONS

Such are some of the strictly scientific results of the low-temperature

work. But there are other results of a more directly practical

kind--neither more important nor more interesting on that account, to

be sure, but more directly appealing to the generality of the

non-scientific public. Of these applications, the most patent and the

first to be made available was the one forecast by Davy from the very

first--namely, the use of liquefied gases in the refrigeration of

foods. Long before the more resistant gases had been liquefied, the more

manageable ones, such as ammonia and sulphurous acid, had been utilized

on a commercial scale for refrigerating purposes. To-day every

brewery and every large cold-storage warehouse is supplied with such

a refrigerator plant, the temperature being thus regulated as is not

otherwise practicable. Many large halls are cooled in a similar manner,

and thus made comfortable in the summer. Ships carrying perishables

have the safety of their cargoes insured by a refrigerator plant. In all

large cities there are ice manufactories using the same method, and of

late even relatively small establishments, hotels, and apartment houses

have their ice-machine. It seems probable that before long all such

buildings and many private dwellings will be provided with a cooling

apparatus as regularly as they are now equipped with a heating

apparatus.

The exact details of the various refrigerator machines of course vary,

but all of them utilize the principles that the laboratory workers first

established. Indeed, the entire refrigerator industry, now assuming

significant proportions, may be said to be a direct outgrowth of that

technical work which Davy and Faraday inaugurated and prosecuted at the

Royal Institution--a result which would have been most gratifying to the

founder of the institution could he have forecast it. The usual means

of distributing the cooling fluids in the commercial plants is by

the familiar iron pipes, not dissimilar in appearance (when not in

operation) to the familiar gas, water, and steam pipes. When operating,

however, the pipes themselves are soon hidden from view by the thick

coating of frost which forms over them. In a moist beer-cellar

this coating is often several inches in thickness, giving a very

characteristic and unmistakable appearance.

Another commercial use to which refrigerator machines are now put is in

the manufacture of various drugs, where absolute purity is desirable.

As different substances congeal at different temperatures, but the same

substances at uniform pressure always at the same temperature, a

means is afforded of freeing a drug from impurities by freezing, where

sometimes the same result cannot be accomplished with like thoroughness

by any other practicable means. Indeed, by this means impurities have

been detected where not previously suspected. And Professor Ramsay has

detected some new elementary substances even, as constituents of the

air, which had previously not been dissociated from the nitrogen with

which they are usually mixed.

Such applications of the refrigerator principles as these, however,

though of vast commercial importance, are held by many enthusiasts to

be but a bagatelle compared with other uses to which liquefied gases

may some time be put. Their expectations are based upon the enormous

potentialities that are demonstrably stored in even a tiny portion of,

say, liquefied air. These are, indeed, truly appalling. Consider, for

example, a portion of air at a temperature above its critical point, to

which, as in Thilorier's experiments, a pressure of thirty-one tons to

the square inch of the encompassing wall is being applied. Recall that

action and reaction are equal, and it is apparent that the gas itself is

pushing back--struggling against being compressed, if you will--with an

equal power. Suppose the bulk of the gas is such that at this pressure

it occupies a cubical space six inches on a side--something like the

bulk of a child's toy balloon, let us say. Then the total outward

pressure which that tiny bulk of gas exerts, in its desperate molecular

struggle, is little less than five thousand tons. It would support an

enormous building without budging a hair's-breadth. If the building

weighed less than five thousand tons it would be lifted by the gas; if

much less it would be thrown high into the air as the gas expanded. It

gives one a new sense of the power of numbers to feel that infinitesimal

atoms, merely by vibrating in unison, could accomplish such a result.

But now suppose our portion of gas, instead of being placed under our

hypothetical building, is plunged into a cold medium, which will permit

its heat-vibrations to exhaust themselves without being correspondingly

restored. Then, presently, the temperature is lowered below the critical

point, and, presto! the mad struggle ceases, the atoms lie amicably

together, and the gas has become a liquid. What a transformed thing

it is now. Instead of pressing out with that enormous force, it has

voluntarily contracted as the five thousand tons pressure could not

make it do; and it lies there now, limpid and harmless-seeming, in the

receptacle, for all the world like so much water.

And, indeed, the comparison with water is more than superficial, for

in a cup of water also there are wonderful potentialities, as every

steam-engine attests. But an enormous difference, not in principle but

in practical applications, exists in the fact that the potentialities

of the water cannot be utilized until relatively high temperatures are

reached. Costly fuel must be burned and the heat applied to the water

before it can avail to do its work. But suppose we were to place our

portion of liquid air, limpid and water-like, in the cylinder of a

locomotive, where the steam of water ordinarily enters. Then, though no

fuel were burned--though the entire engine stood embedded in the snow

of an arctic winter--it would be but a few moments before the liquid air

would absorb even from this cold medium heat enough to bring it above

its critical temperature; and, its atoms now dancing apart once more and

re-exerting that enormous pressure, the piston of the engine would be

driven back and then the entire cylinder burst into fragments as the

gas sought exit. In a word, then, a portion of liquid air has a store

of potential energy which can be made kinetic merely by drawing upon

the boundless and free supply of heat which is everywhere stored in the

atmosphere we breathe and in every substance about us. The difficulty

is, not to find fuel with which to vaporize it, as in case of water,

but to keep the fuel from finding it whether or no. Were liquid air in

sufficient quantities available, the fuel problem would cease to

have any significance. But of course liquid air is not indefinitely

available, and exactly here comes the difficulty with the calculations

of many enthusiasts who hail liquefied gas as the motive power of the

near future. For of course in liquefying the air power has been applied,

for the moment wasted, and unless we can get out of the liquid more

energy than we have applied to it, there is no economy of power in

the transaction. Now the simplest study of the conditions, with the

mechanical theory of matter in mind, makes it clear that this is

precisely what one can never hope to accomplish. Action and reaction are

equal and in opposite directions at all stages of the manipulation, and

hence, under the most ideal conditions, we must expect to waste as much

work in condensing a gas (in actual practice more) as the condensed

substance can do in expanding to the original volume. Those enthusiasts

who have thought otherwise, and who have been on the point of perfecting

an apparatus which will readily and cheaply produce liquid air after

the first portion is produced, are really but following the old

perpetual-motion-machine will-o'-the-wisp.

It does not at all follow from this, however, that the energies of

liquefied air may not be utilized with enormous advantage. It is not

always the cheapest form of power-transformer that is the best for all

purposes, as the use of the electrical storage battery shows. And so it

is quite within the possibilities that a multitude of uses may be

found for the employment of liquid air as a motive power, in which its

condensed form, its transportability or other properties will give

it precedence over steam or electricity. It has been suggested, for

example, that liquefied gas would seem to afford the motive power par

excellence for the flying-machine, once that elusive vehicle is well in

harness, since one of the greatest problems here is to reduce the weight

of the motor apparatus. In a less degree the same problem enters into

the calculations of ships, particularly ships of war; and with them also

it may come to pass that a store of liquid air (or other gas) may come

to take the place of a far heavier store of coal. It is even within the

possibilities that the explosive powers of the same liquid may take the

place of the great magazines of powder now carried on war-ships; for,

under certain conditions, the liquefied gas will expand with explosive

suddenness and violence, an "explosion" being in any case only a very

sudden expansion of a confined gas. The use of the compressed air in the

dynamite guns, as demonstrated in the Cuban campaign, is a step in this

direction. And, indeed, the use of compressed air in many commercial

fields already competing with steam and electricity is a step towards

the use of air still further compressed, and cooled, meantime, to a

condition of liquidity. The enormous advantages of the air actually

liquefied, and so for the moment quiescent, over the air merely

compressed, and hence requiring a powerful retort to hold it, are patent

at a glance. But, on the other hand, the difficulty of keeping it liquid

is a disadvantage that is equally patent. How the balance will be struck

between these contending advantages and disadvantages it remains for

the practical engineering inventors of the future--the near future,

probably--to demonstrate.

Meantime there is another line of application of the ideas which the

low-temperature work has brought into prominence which has a peculiar

interest in the present connection because of its singularly Rumfordian

cast, so to speak, I mean the idea of the insulation of cooled or heated

objects in the ordinary affairs of life, as, for example, in cooking.

The subject was a veritable hobby with the founder of the Royal

Institution all his life. He studied the heat-transmitting and

heat-reflecting properties of various substances, including such

directly practical applications as rough surfaces _versus_ smooth

surfaces for stoves, the best color for clothing in summer and in

winter, and the like. He promulgated his ideas far and wide, and

demonstrated all over Europe the extreme wastefulness of current methods

of using fuel. To a certain extent his ideas were adopted everywhere,

yet on the whole the public proved singularly apathetic; and, especially

in America, an astounding wastefulness in the use of fuel is the general

custom now as it was a century ago. A French cook will prepare an

entire dinner with a splinter of wood, a handful of charcoal, and a

half-shovelful of coke, while the same fuel would barely suffice to

kindle the fire in an American cook-stove. Even more wonderful is the

German stove, with its great bulk of brick and mortar and its glazed

tile surface, in which, by keeping the heat in the room instead of

sending it up the chimney, a few bits of compressed coal do the work of

a hodful.

It is one merit of the low-temperature work, I repeat, to have called

attention to the possibilities of heat insulation in application to "the

useful purposes of life." If Professor Dewar's vacuum vessel can reduce

the heat-transmitting capacity of a vessel by almost ninety-seven per

cent., why should not the same principle, in modified form, be applied

to various household appliances--to ice-boxes, for example, and

to cooking utensils, even to ovens and cook-stoves? Even in the

construction of the walls of houses the principles of heat insulation

might advantageously be given far more attention than is usual at

present; and no doubt will be so soon as the European sense of economy

shall be brought home to the people of the land of progress and

inventions. The principles to be applied are already clearly to hand,

thanks largely to the technical workers with low temperatures. It

remains now for the practical inventors to make the "application to the

useful purposes of life." The technical scientists, ignoring the example

which Rumford and a few others have set, have usually no concern with

such uninteresting concerns.

For the technical scientists themselves, however, the low-temperature

field is still full of inviting possibilities of a strictly technical

kind. The last gas has indeed been liquefied, but that by no means

implies the last stage of discovery. With the successive conquest of

this gas and of that, lower and lower levels of temperature have been

reached, but the final goal still lies well beyond. This is the north

pole of the physicist's world, the absolute zero of temperature--the

point at which the heat-vibrations of matter are supposed to be

absolutely stilled. Theoretically this point lies 2720 below the

Centigrade zero. With the liquefaction of hydrogen, a temperature of

about -253 deg or -254 deg Centigrade has been reached. So the gap

seems not so very great. But like the gap that separated Nansen from the

geographical pole, it is a very hard road to travel. How to compass it

will be the study of all the low-temperature explorers in the immediate

future. Who will first reach it, and when, and how, are questions for

the future to decide.

And when the goal is reached, what will be revealed? That is a question

as full of fascination for the physicist as the north-pole mystery

has ever been for the generality of mankind. In the one case as in

the other, any attempt to answer it to-day must partake largely of the

nature of a guess, yet certain forecasts may be made with reasonable

probability. Thus it can hardly be doubted that at the absolute zero all

matter will have the form which we term solid; and, moreover, a degree

of solidity, of tenacity and compactness greater than ever otherwise

attained. All chemical activity will presumably have ceased, and any

existing compound will retain unaltered its chemical composition so

long as absolute zero pertains; though in many, if not in all cases,

the tangible properties of the substance--its color, for example, and

perhaps its crystalline texture--will be so altered as to be no longer

recognizable by ordinary standards, any more than one would ordinarily

recognize a mass of snowlike crystals as air.

It has, indeed, been suggested that at absolute zero all matter may take

the form of an impalpable powder, the forces of cohesion being destroyed

with the vibrations of heat. But experiment seems to give no warrant to

this forecast, since cohesion seems to increase exactly in proportion

to the decrease of the heat-vibrations. The solidity of the meteorites

which come to the earth out of the depths of space, where something

approaching the zero temperature is supposed to prevail, also

contradicts this assumption. Still less warrant is there for a visionary

forecast at one time entertained that at absolute zero matter will

utterly disappear. This idea was suggested by the observation, which

first gave a clew to the existence of the absolute zero, that a gas at

ordinary temperatures and at uniform pressure contracts by 1-27 2d of

its own bulk with each successive degree of lowered temperature. If this

law held true for all temperatures, the gas would apparently contract to

nothingness when the last degree of temperature was reached, or at least

to a bulk so insignificant that it would be inappreciable by standards

of sense. But it was soon found by the low-temperature experimenters

that the law does not hold exactly at extreme temperatures, nor does it

apply at all to the rate of contraction which the substance shows after

it assumes the liquid and solid conditions. So the conception of the

disappearance of matter at zero falls quite to the ground.

But one cannot answer with so much confidence the suggestion that at

zero matter may take on properties hitherto quite unknown, and making

it, perhaps, differ as much from the conventional solid as the solid

differs from the liquid, or this from the gas. The form of vibration

which produces the phenomena of temperature has, clearly, a determining

share in the disposal of molecular relations which records itself to our

senses as a condition of gaseousness, liquidity, or solidity; hence it

would be rash to predict just what inter-molecular relations may not

become possible when the heat-vibration is altogether in abeyance. That

certain other forms of activity may be able to assert themselves in

unwonted measure seems clearly forecast in the phenomena of increased

magnetism, and of phosphorescence at low temperatures above outlined.

Whether still more novel phenomena may put in an appearance at the

absolute zero, and if so, what may be their nature, are questions that

must await the verdict of experiment. But the possibility that this may

occur, together with the utter novelty of the entire subject, gives

the low-temperature work precedence over almost every other subject

now before the world for investigation (possible exceptions being

radio-activity and bacteriology). The quest of the geographical pole is

but a child's pursuit compared with the quest of the absolute zero. In

vital interest the one falls as far short of the other as the cold of

frozen water falls short of the cold of frozen air.

Where, when, and by whom the absolute zero will be first reached are

questions that may be answered from the most unexpected quarter. But it

is interesting to know that great preparations are being made today in

the laboratories of the Royal Institution for a further attack upon the

problem. Already the research equipment there is the best in the world

in this field, and recently this has been completely overhauled and

still further perfected. It would not be strange, then, in view of past

triumphs, if the final goal of the low-temperature workers should be

first reached in the same laboratory where the outer territories of

the unknown land were first penetrated three-quarters of a century ago.

There would seem to be a poetic fitness in the trend of events should it

so transpire. But of course poetic fitness does not always rule in the

land of science.

IV. SOME PHYSICAL LABORATORIES AND PHYSICAL PROBLEMS

SIR NORMAN LOCKYER AND SOLAR CHEMISTRY