stretches to a greater or less length from its bright head or “nucleus.”
A large comet, when seen to greatest advantage, may have a tail which
stretches across one-third of the “vault of heaven,” and may be reckoned
by astronomers at as much as one hundred and twenty million miles long.
Donati’s comet—which some of my readers will remember, as I do, when it
visited us in 1858—was of this imposing size. Halley’s comet, on the
other hand, when it was last “here,” namely, in 1835, showed a tail
estimated by astronomers to be fifty million miles long. The tail was
more than twice as long when Halley’s comet appeared in 1456. There was
a big comet “on view” in 1811—the year celebrated for its wine—and in
recent times a fine comet appeared in 1861, and another (Coggia’s comet)
in 1874.
The ancient records of comets are naturally full of exaggeration. Up to
Milton’s time—two hundred and fifty years ago—they caused the greatest
terror and excitement by their sudden appearance in the sky. This is due
to the fact that mankind from the very earliest periods of which we have
record has not merely gazed at the “starry host” by night in solemn
wonder, but even in early prehistoric times studied and watched the
stars so as to know much of their movements and regular comings and
goings. The earliest priests, the earliest “wise men,” were those who
knew the stars and could fix the seasons by their place; the earliest
temples—Stonehenge, and others older still—were star-temples or
observatories, and their priests were astronomers. To such a pitch did
reverence for star-knowledge attain that our ancestors confused the
astral signs of changing season and cycle with the cause itself of
change, and attributed all kinds of mundane events and each man’s fate
to “the influence of the stars.” Hence the sudden appearance of a
flaming comet was held to be a portent, and was always supposed either
to foretell or even to produce some very unpleasant event, such as a big
war or a pestilence, or the death of some one supposed to be of
consequence. The earliest Greek poetry enshrines the superstition, which
is handed on by Virgil, and finally by Milton. In Pope’s translation of
the _Iliad_ we find the helmet of the terrible Achilles described as
shining
“Like the red star, that from his flaming hair
Shakes down diseases, pestilence, and war.”
And Milton, in 1665, in his _Paradise Lost_, wrote—
“On th’other side,
Incenst with indignation, Satan stood
Unterrifi’d; and like a comet burn’d,
That fires the length of Ophiuchus huge
In th’ Arctic sky, and from his horrid hair
Shakes pestilence and war.”
In this year of the celebration of the tercentenary of Milton’s birth,
it is not a little curious to find that John Milton, himself a scholar
of St. Paul’s School, wrote those lines when Edmund Halley, the future
Astronomer Royal, had just entered the same great school, then standing
in St. Paul’s Churchyard, as it did when I was “one of the fishes,” and
used to see men hanging in the Old Bailey—I once saw five[5]—on
Monday mornings as I passed on my way to the school. To a Pauline it is
not without significance that the return of Halley’s comet is awaited
within a year of Milton’s tercentenary, and that the greatest astronomer
and the greatest poet of their age were London boys and Paulines.
Ancient records tell of comets of gigantic size, of the shape of a
sword, the head as big as the moon, and so on. There is no reason to
suppose that within historic times there have been any much bigger than
that of 1858. Milton, in the lines above quoted, was not referring to an
imaginary comet, but to one which actually did appear when he was a boy
of ten (1618), in the constellation called Ophiuchus. It was of enormous
size, the tail being recorded as longer even than that of 1858. It was
held responsible by educated and learned men of the day for disasters.
Evelyn says in his diary, “The effects of that comet, 1618, still
working in the prodigious revolutions now beginning in Europe,
especially in Germany.” The comet of 1665 was, with equal assurance,
regarded as the cause of the Great Plague of London. In that year was
published the first number of the _Philosophical Transactions_ of the
Royal Society of London, then recently founded “for the promotion of
natural knowledge.” It contains an account of a paper by a learned
French gentleman, M. Auzout, in which an attempt is made to predict the
movements among the stars of the comet of 1664. Astronomers had long
known and been able to predict the movements of the planets and the
swinging of the constellations, but, as the French author observes, “all
the world had been hitherto persuaded that the motions of comets were so
irregular that they could not be reduced to any laws.” He also hoped, by
examining the movements of the comets of 1664 and 1665, to determine
“the great question whether the earth moves or not.” At that time the
earth was “suspected” to move round the sun, but no proof of that motion
had been given. M. Auzout did not succeed in his laudable attempt,
simply because Newton’s great discovery of the law of gravitation had
not then been made.
Edmund Halley was the intimate friend and passionate admirer of Newton.
He paid out of his own pocket for the publication of Newton’s
_Principia_ by the Royal Society in 1686, the society having expended
all its available funds in printing a great work on _Fishes_ (which
shows how at the first, as now, the society cared for the whole range of
the study of Nature). Halley was able to show that comets move regularly
round the sun, in obedience to the same law of gravitation which
controls the movements of the planets and of our earth itself; so that
many of them are regular members of the solar system. Halley especially
calculated out the form of the orbit of the comet of 1682 as an ellipse,
and the time of its journey and recurrence, or “period,” as it is
called, which he showed to be about seventy-five or seventy-six years.
He predicted its recurrence in 1758. Halley died in 1742, at the ripe
age of eighty-six, having, amongst other good deeds, founded the Royal
Society Club, which still dines every Thursday in the session. His comet
reappeared in 1759, a few months later than he had, owing to incomplete
details used in his calculation, expected; but the accuracy of his
scheme of its movement was demonstrated. It duly appeared again in 1835,
and it is now awaited in the spring of 1910. Halley himself had
identified his comet with that of 1607 and of 1531, and lately, by the
aid of records from an ancient seat of astronomical observation—actually
from China—it has been traced back to the month of May in the year 240
B.C. It has caused consternation and terror times enough since then, of
some of which we have record. Finally, it has become the leading
instance of the triumph of scientific knowledge and accuracy over
ignorance and superstition. Halley’s comet caused great alarm in Rome in
the year 66 A.D. A thousand years later (1066) it was seen when William
the Conqueror was preparing to descend on the coast of England, and is
actually represented in the Bayeux tapestry. A number of men are drawn
(or rather “stitched”), with fingers pointed and eyes raised to a shape
in the sky which resembles a star-fish with a large triangular-ribbed
petticoat attached to it, ending in eight flames or tongues (Fig. 45).
The picture is labelled “Isti mirant stella.” There is now no doubt, as
accurate calculations have demonstrated, that William the Conqueror’s
“star” was Halley’s comet—a fact which must give its reappearance in
1910 an additional interest in the eyes of Englishmen.
The shape given to the representations of stars in old pictures and
engravings is a puzzle. Why do they represent a star by the shape of a
star-fish? No star ever looks like that, or produces a picture of that
shape on the retina. The thing is purely conventional. The shape which
we call “star-shaped”—a term we apply to flowers and other things—is
not in the least like a real star as seen by an unprejudiced person.
What one really sees is an ill-defined point of light. The pretended
conventional star of ancient drawings perhaps arose from the simple
artifice of picturing tongue-like flames around or upon any
representation of a fire or a source of light—“to show what it was
meant to be.” Then the notions of perfection and symmetry in regard to
the celestial bodies led to the “tongues” being arranged for the
purposes of draughtsmanship as perfectly symmetrical-pointed rays of a
six- or eight-limbed geometrical design—and latterly it is possible
that the mystical figure known as the “pentacle” was utilised by
astrologers and others as the emblem of a star. However they arose,
neither the weird and astonishing representations of mediæval times nor
the geometrical decorative “stars” of later date seem to have any
relation to an attempt to represent a star as it really appears to the
human eye and the interpreting brain behind it.
[Illustration: FIG. 45.—Copied from a portion of the Bayeux Tapestry,
showing Harold’s men looking with superstitious wonder at the comet
which appeared in the heavens immediately before the departure of
William the Conqueror’s expedition to England in A.D. 1066. That comet
was none other than Halley’s comet, and has now returned, and is visible
from the earth for the twelfth time since the Conquest. (From a lecture
on Halley’s comet, delivered in 1908, by Professor H. H. Turner, F.R.S.,
Halley’s successor in Oxford, published by the Clarendon Press.)]
The orbits of comets, says Professor Turner, of Oxford, in a delightful
lecture delivered in Dublin in the summer of 1908, from which I have
culled many interesting facts and presented them to my readers, “differ
from those of the planets in being far more highly elliptical. Our own
path round the sun is nearly a circle, so that our distance from him
remains nearly the same all the year round; but the distance of a comet
from the sun varies greatly from ‘perihelion,’ when it is near, and
consequently bright, to ‘aphelion,’ when he is so distant and faint that
we lose sight of him.” The sun is not at the centre of the ellipse
described by a comet’s path, but is quite near to one end of it, so that
comets approach the sun far more closely than do the planets, some
taking so close a turn round the sun that the heat from it to which they
are exposed is 2000 times as great as that which the earth receives. If
the orbit of a comet is really elliptic, then there at last comes a
time, though it may be only after thousands of years, when the comet,
having rounded the sun at close quarters, and journeyed off into space,
has his journey brought to a turning-point at the other end of the
ellipse, and begins to draw near again, advancing towards the sun. The
length of the orbit of Halley’s comet is about 3255 million miles, and
the breadth at its broadest is about 800 million miles, and he takes
about thirty-eight years to travel the full length (along the curve) and
thirty-eight years to come back again! Other comets have other lengths
and breadths of orbit, and take longer or shorter periods to go round.
But the conditions of attraction affecting a comet may be such that the
return journey never occurs. They may be such that the comet goes on
indefinitely travelling away from our sun, until he is caught by some
other star, and his orbit changes its shape, with the new sun as
attracting centre. These are the “wandering comets” as distinct from the
“periodic comets,” which have been shown to conform to Halley’s scheme
of their movement and recurrence.
And now some one will ask, perhaps impatiently, “What, after all, is a
comet?” We have seen that many are continuously, and others casually,
members of the solar system. What do they consist of? Spectrum-analysis
shows that they consist chiefly of the chemical element carbon.[6]
Though they have weight, and are attracted by the sun, yet they seem to
be for all their size and terrifying shape and glare incredibly light
and airy things. Herschel declared that the tail of a big comet
probably consisted of but two or three pounds of solid matter—diffused,
rarefied, and luminous. And the head or nucleus certainly does not weigh
many hundreds of tons. In the eighteenth century astronomers observed a
comet pass right in among the moons of the planet Jupiter. You might
expect the moons to be terribly knocked about by such an impact. They
were not; they were not deflected in the smallest appreciable degree
from their position and regular movement! One is naturally inclined to
look upon the tail of a comet as something like the smoke of a railway
engine trailing behind the advancing “head.” As a matter of fact, it
does not always trail behind, but is always turned away from the sun, so
that when the comet is travelling away from the sun the tail is in
front! It is now held that the tail is caused by the radiant energy
(light and heat) of the sun, blowing, as it were, the lighter particles
from the incandescent head, and causing them to spread out in a long
track of variable shape. The photographs of the third comet of the year
1908 show that the tail can vary to an astonishing extent and with great
rapidity—that is to say, in four or five hours. It is seen in those
photographs as a scimitar-like curved blade, then with a second head or
nucleus behind the leading one, then actually bent like the letter Z,
and then divided into seven distinct diverging “plumes,” and then it
returns to its former simple shape—all in the course of a few days.
Astronomers have now shown that there is a close connection between
comets and the showers of “shooting stars” or meteors which frequently
strike the earth’s atmosphere. It is considered probable that comets
eventually break down into streams of meteors, and that their “life” (if
one may use that term) is, relatively to that of other heavenly bodies
(which are all undergoing change and, in many cases, decay), not a very
long one. But there are no facts at present known which enable us to
tell whether a given comet is young or old, and it would have been a
decided shock had it been found that Halley’s comet, which has so
happily spent every seventy-sixth year with us for so many centuries,
had “burst up,” or by “indisposition” had been unable to pay his usual
visit as expected in 1910.
FOOTNOTES
[5] The pirates of the _Flowery Land_.
[6] I am indebted to Mr. Rolston, of the Solar Physics Observatory,
South Kensington, for some information on this matter.
Generally speaking, it appears that the spectra of these bodies indicate
carbon—in some form—as the principal constituent.
As to the particular form of carbon, there is still a considerable
doubt, so much that, in describing the spectrum of Morehouse’s comet,
Professor Frost says (_Astrophysical Journal_, xxix., p. 59, 1909):—“We
avoid the still unsettled question of the ‘carbon’ bands (of the
so-called ‘Swan’ spectrum) which have been so often ascribed to a
hydrocarbon, specifically acetylene, and we use for them the simple
designation ‘carbon.’”
In addition to this “carbon” there is the cyanogen spectrum present in
most cases.
Sodium and iron have been detected in the spectra of some few comets,
_e.g._ Wells (1882, ii.), whilst Holmes (1892) showed only continuous
spectrum.
An interesting suggestion is made by Newall, namely, that the spectrum
is not indicative of the _comet’s_ composition, but of that of the
medium through which the body passes. Thus the persistent identification
of the cyanogen bands in cometary spectra is attributed, primarily, to
the “heating up” of cyanogen existing, free, in circum-solar space.
Till 1907 most of the cometary spectrograms showed only the “carbon” and
cyanogen radiations, but in Daniel’s comet of that year, and in
Morehouse’s of 1909, other lines were detected for which origins have
not, as yet, been found.
Thus, some form of carbon + unknown + (occasionally) sodium and iron
seems to sum up our present knowledge of cometary composition.
XXV
ABOUT CHOLERA
What is this terrible disease which every few years travels from the
banks of the Indian Ganges, where it is always present, and makes its
way to one or more of the great cities of Europe, killing its thousands
with horrifying rapidity? The word “cholera” is used by the great Greek
physician of antiquity, Hippocrates, and by his followers down to the
days of our own Sydenham, to describe a malady which occurs commonly in
summer, is often of severe character, but rarely fatal, and is
characterised by the exudation from the walls of the intestine of
copious fluid, usually accompanied by vomiting and sometimes by
“cramps.” This malady is now distinguished by physicians as “simple
cholera,” or European cholera, the last name being misleading, since the
disease occurs all over the world. It is caused by a special microbe,
which multiplies in the intestines and produces a poison. Other microbes
produce similar results. One which causes luminosity in foul salt water
has been found to produce cholera-like results when cultivated in a
state of purity and swallowed by man. Other poisons besides those
produced by microbes set up a sort of “cholera” in animals and man.
Drugs of both mineral and vegetable origin have this effect, as every
one knows, and are used in small quantities to produce purging.
Microbes which are noted for other obvious effects which they produce by
the poisons they form in man’s intestines—such as the microbe of
typhoid fever—also produce cholera-like purging.
But the name “cholera,” or “the cholera,” is now applied without any
further qualification to what would be more correctly described as
“Indian cholera,” or “epidemic cholera.” It is a disease which first
became known to Europeans in India in 1817, less than a hundred years
ago. It resembles “simple” cholera in its general features, but is
usually much more violent in its attack, and often causes complete
collapse in two or three hours from its onset, and death in as many
more. The main point about it is, however, that it is a quickly
spreading “epidemic” disease; it invades a whole population, and travels
from place to place along definite routes. Although the outbreak of
cholera in India in 1817 was the first to attract the attention of
Europeans, it was nothing new in India, and was recognised in distant
ages by Hindu writers. Its usual name on the delta of the Ganges is
“medno-neidan.” Ninety per cent. of the population perished of cholera
in some districts of India in 1817, and English troops were attacked by
it with terrible results.
Cholera gradually made its way in subsequent years through Persia to
Russia, and at last to Western Europe; but it was not until late in the
year 1831 that Indian cholera arrived for the first time in England, and
in the following year it caused something like a panic. There have been
at least three subsequent outbursts of Indian cholera (before that of
the year 1908) which have reached Europe, and two of these have reached
England and caused profound alarm and anxiety. That in 1854 reached us
just before the Crimean War, and caused such rapid and numerous deaths
in London, especially in the West End (St. James’s, Westminster), that
the corpses were removed in carts as in the days of the plague. It was
then that the Broad Street pump became famous, and the carefully
demonstrated history of a cesspool leaking into the well of the pump, of
the existence of a cholera patient in the house to which the cesspool
was attached and of the infection with cholera of healthy people who
sent all the way from Hampstead to fetch what they thought was the
beautifully pure, cool, and palatable water of Broad Street, St.
James’s, caused a most vivid and salutary impression on the public mind.
The “water-carriage” of the cholera infection was established as a fact,
and the subsequent abolition of surface wells and pumps, as well as of
cesspools, in London and other cities was the result. Indeed, the active
development of sanitation and sanitary measures of all kinds in Great
Britain may be traced to the panic caused by the cholera in 1854 and to
the well-founded conviction that it was in the power of the community,
by the construction of sewers and the provision of untainted
water-supply, to protect itself against such disaster in the future.
Years passed by, and still the actual germ of cholera was unknown. In
India it was not even admitted that its diffusion was especially
connected with water-supply. The methods of observing with the
microscope those minute swarming organisms which are called “bacteria”
became immensely improved. They were isolated, cultivated in purity, and
the activity of a vast number of different kinds of different shapes,
sizes, and modes of growth was ascertained. They were distinguished
according to their shape as bacilli, spirilla, micrococci, and so on,
and separate kinds were characterised—one producing ordinary
putrefaction, another the souring of milk, another the “cheesing” of the
same fluid, another the destruction of teeth and of bone, another the
terrible anthrax of cattle or wool-sorters’ disease, another (a spiral
thread in the blood this!) the recurrent fever of East Europe—each
producing its own special poison or other chemical substance.
So it went on till Koch, of Berlin, discovered the bacillus of tubercle
and Hansen that of leprosy. Others had failed to find what Koch now
found as the result of a special mission on behalf of the German
Imperial Government to India (undertaken as nearly as I can recollect
about the year 1884)—namely, the living organism (Fig. 46) which by its
growth in man’s intestine causes Indian cholera. Koch found a spiral
threadlike “bacterium” in cholera patients, which readily breaks up into
little curved segments like a comma (each less than the one
ten-thousandth of an inch in length), and swarms by the million in the
intestines of such patients. He showed that it can be cultivated in
dilute gelatinised broth, and obtained in spoonfuls. It was, however,
only with great difficulty that he could produce cholera in animals by
administering this pure concentrated growth of cholera germs to them.
Then a most courageous thing was done. A great and very acute
investigator of cholera in Munich, Pettenkofer by name—who did not
believe that Koch’s comma-bacillus was really the effective germ of
cholera—himself swallowed a whole spoonful—many millions—of the
cultivated cholera germ. His assistants did the same—and none of them
suffered any ill effect! Few, if any, of the investigators of this
question gave up, as a consequence, their conviction that Koch’s
bacillus was the real and active cause of cholera. They supposed that it
must be necessary for the human intestine to be in a favourable
condition—an unhealthy condition—for the Koch’s bacillus to multiply
in it. It was by this time known that bacteria of all kinds are
exceedingly sensitive in regard to the acidity or alkalinity, the
oxygenation or de-oxygenation of the fluids and organic substances in
which they can, when exactly suited, multiply with tremendous rapidity.
Thus the tubercle bacillus cannot be cultivated on pure blood-serum, but
if a trace of glycerine be added to the serum the tubercle bacillus
grows, divides, multiplies like yeast in a brewing-vat. A little later
Pettenkofer’s audacious experiment was repeated by Dr. Metchnikoff in
Paris. He swallowed a cultivated mass of the cholera germ on three
successive days, and had no injurious result. Others in his laboratory
did the same, with the result of only a slight intestinal disturbance.
But of a dozen who thus put the matter to the proof in the Institut
Pasteur, one individual acquired an attack of true Indian cholera,
accompanied by all the most violent symptoms, which very nearly caused
his death. This experiment put an end to all discussion, and
demonstrated, once for all, that the comma-bacillus (or spirillum) of
Koch is really capable of producing Indian cholera, and is the actual
agent of this disease.