Sir Humphry Davy suggests a chemical method for unrolling
the ancient Papyri.--He is encouraged by the Government
to proceed to Naples for that purpose.--He embarks at
Dover.--His experiments on the Rhine, the Danube, the Raab,
the Save, the Ironzo, the Po, and the Tiber, in order to
explain the formation of mists on rivers and lakes.--His
arrival and reception at Naples.--He visits the excavations
at Herculaneum.--He concludes that it was overwhelmed by
sand and ashes, but had never been exposed to burning
matter.--He commences his attempt of unrolling the Papyri.--His
failure.--He complains of the persons at the head of the
department in the Museum.--He analyses the waters of the
Baths of Lucca.--His return to England.--Death of Sir Joseph
Banks.--He is elected President of the Royal Society.--Some
remarks on that event.--He visits Penzance.--Is honoured by
a public dinner.--Electro-magnetic discoveries of Oersted
extended by Davy.--He examines Electrical Phenomena in
vacuo.--The results of his experiments questioned.--He enquires
into the state of the water, and aëriform matter in the
cavities of crystals.--The interesting results of his enquiry
confirm the views of the Plutonists.
Our history now proceeds to exhibit Sir Humphry Davy in quite a new
field of enquiry;--engaged in investigating, amidst the ruins of
Herculaneum, the nature and effects of the volcanic eruption which
overwhelmed that city in the reign of Titus; and in attempting, by
the resources of modern science, to unfold and to render legible
the mouldering archives which have been recovered from its
excavations, and deposited in the Museum at Naples.
Having witnessed the unsuccessful attempts of Dr. Sickler to unroll
some of the Herculaneum manuscripts, it occurred to him that a
chemical examination of their nature, and of the changes they had
undergone, might suggest some method of separating the leaves from
each other, and of rendering legible the characters impressed
upon them. On communicating this opinion to Sir Thomas Tyrwhitt,
he immediately placed at his disposal fragments which had been
operated upon by Mr. Hayter and by Dr. Sickler: at the same time,
Dr. Young presented him with some small pieces, which he himself
had formerly attempted to unroll.
Davy was very soon convinced by the products of their distillation,
that the nature of these manuscripts had been generally
misunderstood; that they had not, as was usually supposed, been
carbonized by the operation of fire, but were in a state analogous
to peat, or to Bovey coal, the leaves being generally cemented
into one mass by a peculiar substance which had formed, during the
fermentation and chemical change of the vegetable matter composing
them, in a long course of ages. The nature of this substance being
once known, the destruction of it would become a subject of obvious
chemical investigation.
It occurred to him, that as chlorine and iodine do not exert any
action upon pure carbonaceous substances, while they possess a
strong attraction for hydrogen, these bodies might probably be
applied with success for the purpose of destroying the adhesive
matter, without the possibility of injuring the letters of the
Papyri, the ink of the ancients, as it is well known, being
composed of charcoal. He accordingly exposed a fragment of a
brown manuscript, in which the layers were strongly adherent, to
an atmosphere of chlorine; there was an immediate action, the
papyrus smoked, and became yellow, and the letters appeared much
more distinct. After which, by the application of heat, the layers
separated from each other, and fumes of muriatic acid were evolved.
The vapour of iodine had a less distinct, but still a very sensible
action. By the simple application of heat to a fragment in a close
vessel filled with carbonic acid, or with the vapour of ether,
so regulated as to raise the temperature very gradually, and as
gradually to reduce it, there was a marked improvement in the
texture of the papyrus, and its leaves were more easily unrolled.
In all these preliminary trials, however, he found that the success
of the experiment absolutely depended upon the nicety with which
the temperature was regulated.
Different papyri having exhibited different appearances, he
concluded that the same process would not apply in all cases; but
even a partial success he considered as a step gained, and it
served to increase his anxiety to examine in detail the numerous
specimens preserved in the Museum at Naples, as well as to visit
the excavations that still remained open at Herculaneum.
Mr. Hamilton, to whom these views were communicated, with that
ardour which belongs to his character, entered warmly into a plan
which might enable Sir Humphry Davy to accomplish his objects; and
on his representation of them, the Earl of Liverpool and Viscount
Castlereagh placed at his disposal such funds as were requisite for
paying the persons whom it was necessary to engage in the process.
At the same time, Sir Humphry Davy had the honour of an audience
of his late Majesty, then Prince Regent; and on witnessing the
results, his Royal Highness was pleased to express his approbation,
and graciously condescended to patronize the undertaking. Exulting
in the prospect of success, and sanguine as to the importance
of its results to literature, Davy embarked at Dover for the
Continent, in order to proceed to Naples, on the 26th of May 1818.
During his journey, he was engaged in making observations on the
comparative temperature of air incumbent upon land and water,
with a view to account for the formation of mists over the beds
of rivers and lakes. The results of this enquiry were embodied in
a memoir, which was read before the Royal Society on the 25th of
February 1819, and published in the Philosophical Transactions
of that year. This paper, while it records the course of his
observations, informs us of the direction of his route to the
southern shores of Italy.
On the 31st of May, while passing along the Rhine from Cologne to
Coblentz, we find him examining the relative temperature of the
air, and of the water of that river. On the 9th, 10th, and 11th of
June, he was making similar observations on the Danube, during
a voyage from Ratisbonne to Vienna. On the 11th of July, he was
similarly engaged on the Raab, near Kermond in Hungary. In the
end of August he was on the Save in Carniola; in the middle of
September on the Ironzo in the Friul; in the end of that month, on
the Po, near Ferrara; and in the beginning of October, repeatedly
on the Tiber, and on the small lakes in the Campagna of Rome,
extending and multiplying his observations upon the formation of
mists: from the results of which he established the law, that the
formation of mist, on a river or lake, never takes place, if the
temperature of the water be lower than that of the atmosphere; not
even though the latter should be even saturated with vapour.
Possessed of this fact, he was enabled to explain a phenomenon
which all persons who have been accustomed to the observation of
Nature must have frequently witnessed, although it had never yet
been philosophically explained, nor even fully discussed, viz.--the
formation of mists over the beds of rivers and lakes, in calm and
clear weather, after sunset.
Sir Humphry Davy thinks that whoever has considered the phenomena
in relation to the radiation and communication of heat and nature
of vapour, since the publication of the researches of MM. Rumford,
Leslie, Dalton, and Wells, can scarcely have failed to discover
their true causes.
"As soon as the sun has disappeared from any part of the globe,
the surface begins to lose heat by radiation, and in greater
proportions as the sky is clearer; but the land and water are
cooled by this operation in a very different manner: the
impression of cooling on the land is limited to the surface, and
very slowly transmitted to the interior; whereas in water above 45°
Fah., as soon as the upper stratum is cooled, whether by radiation
or evaporation, it sinks in the mass of fluid, and its place is
supplied by warmer water from below, and till the temperature of
the whole mass is reduced nearly to 40°, the surface cannot be
the coolest part.[62] It follows, therefore, that wherever water
exists in considerable masses, and has a temperature nearly equal
to that of the land, or only a few degrees below it, and above 45°
at sunset, its surface during the night, in calm and clear weather,
will be warmer than that of the contiguous land; and the air above
the land will necessarily be colder than that above the water; and
when they both contain their due proportion of aqueous vapour, and
the situation of the ground is such as to permit the cold air from
the land to mix with the warmer air above the water, mist or fog
will be the result; which will be so much the greater in quantity,
as the land surrounding or inclosing the water is higher, the water
deeper, and the temperature of the water, which will coincide with
the quantity or strength of vapour in the air above it, greater."
[62] Water, when cooled down to 40°, expands in volume, and thus
becomes specifically lighter; and therefore at that temperature
remains at the surface.
It will be remembered, that the rivers Inn and Ilz flow into
the Danube below Passau; a circumstance which afforded Davy
an excellent opportunity of confirming, by observation and
experiment, the truth of his theory. On examining the temperature
of these rivers, at six o'clock A. M. June 11, that of the Danube
was found to be 62°, that of the Inn 56.5°, and that of the Ilz
56°: the temperature of the atmosphere on the banks, where their
streams mixed, was 54°. The whole surface of the Danube was covered
with a thick fog; on the Inn there was a slight mist; and on the
Ilz barely a haziness, indicating the deposition of a very small
quantity of water. About one hundred yards below the conflux of
the rivers, the temperature of the central part of the Danube was
59°; and here the quantity of mist was less than on the bed of the
Danube before the junction; but about half a mile below, the warmer
water had again found its place at the surface, and the mist was as
copious as before the union of the three rivers.
After mists have been formed above rivers and lakes, Davy considers
that their increase may not only depend upon the constant operation
of the cause which originally produced them, but likewise upon the
radiation of heat from the superficial particles of water composing
the mist, which produces a descending current of cold air in the
very body of the mist, while the warm water continually sends up
vapour. It is to these circumstances, he says, that the phenomena
must be ascribed of mists from a river or lake sometimes arising
considerably above the surrounding hills. He informs us that he
had frequently witnessed such an appearance during the month of
October, after very still and very clear nights, in the Campagna of
Rome above the Tiber, and on Monte Albano, over the lakes existing
in the ancient craters of this extinguished volcano; and in one
instance, on the 17th of October, before sunrise, there not being a
breath of wind, a dense white cloud, of a pyramidal form, was seen
on the site of Alban Lake, and rising far above the highest peak of
the mountain. Its form gradually changed after sunrise; its apex
first disappeared, and its body, as it were, melted away in the
sunbeams.
Great dryness of the air, or a current of dry air passing across
a river, he found, as we might have expected, to prevent the
formation of mist even when the temperature of the water was much
higher than that of the atmosphere.
Thus did our philosopher, during the course of his journey to
Naples, by a series of observations and experiments, investigate
a phenomenon connected with the deposition of water from the
atmosphere, and which is not without an effect in the economy of
nature; for verdure and fertility, in hot climates, generally
follow the courses of rivers, and by the operation of the law he
established, they are extended to the hills, and even to the plains
surrounding their banks.
On his arrival at Naples, Sir H. Davy found that a letter from his
Royal Highness the Prince Regent to the King, and a communication
made from the Secretary of State for Foreign Affairs to the
Neapolitan Government, had prepared the way for his enquiries, and
procured for him every possible facility in the pursuit of his
objects.
The different rolls of papyri presented very various appearances.
They were of all shades, from a light chestnut brown to a deep
black; some externally were of a glossy black, like jet, which
the superintendents called "varnished;" several contained the
umbilicus, or rolling-stick, in the middle, converted into dense
charcoal. In their texture, also, they were as various as in their
colours.
The persons to whom the care of these MSS. are confided, or who
have worked upon them, have always attributed these different
appearances to the action of fire, more or less intense, according
to the proximity of the lava, which has been imagined to have
covered the part of the city in which they were found; but the
different conclusion at which Davy had arrived, from a chemical
examination in England, was confirmed by a visit to the excavations
that still remained open at Herculaneum.
These excavations are in a loose _tufa_, composed of sand, volcanic
ashes, stones, and dust, cemented by the operation of water, which,
at the time of its action, was probably in a boiling state. The
theatre, and the buildings in the neighbourhood, are incased in
this _tufa_, and, from the manner in which it is deposited in the
galleries of the houses, there can be little doubt that it was
the result of torrents laden with sand and volcanic matter, and
descending, at the same time, with showers of ashes and stone still
more copious than those that covered Pompeii. The excavation in
the house in which the MSS. were found, had been filled up; but
a building, which was said by the guides to be this house, and
which, as is evident from the engraved plan, must at least have
been close to it, at once convinced Davy that the parts nearest
the surface, and, _à fortiori_, those more remote from it, had
never been exposed to any considerable degree of heat. He found a
small fragment of the ceiling of one of the rooms, containing lines
of gold leaf and vermilion, in an unaltered state, which never
could have happened had they been acted upon by any temperature
sufficiently great to convert vegetable matter into charcoal.
The different states of the MSS. exactly coincide with this view,
and furnish evidence of their having undergone a gradual process
of decomposition. The loose chestnut papyri, he observes, were
probably never wetted, but merely changed by the reaction of their
elements, assisted by the operation of a small quantity of air; the
black ones, which easily unroll, may be supposed to have remained
in a moist state, without any percolation of water; while it is
likely that the dense ones, containing earthy matter, have been
acted on by warm water, which not only carried into the folds
earthy matter suspended in it, but likewise dissolved the starch
and gluten used in preparing the papyrus and the glue of the ink,
and distributed them through the substance of the MSS.
As many of the papyri appear to have been strongly compressed when
moist, in different positions, he thinks it probable that they
had been placed on shelves of wood, which were broken down when
the roofs of the houses yielded to the superincumbent mass. That
the operation of fire is not at all necessary for producing such
an imperfect carbonization of vegetable matter as that displayed
by the MSS., is at once proved by an inspection of the houses at
Pompeii, which was covered by a shower of ashes that must have
been cold, as they fell at the distance of seven or eight miles
from the crater of Vesuvius; and yet the wood of its buildings
is uniformly found converted into charcoal, while the colours on
the walls, most of which would have been destroyed or altered by
heat, are perfectly fresh. Where papyri have been found in these
houses, they have appeared in the form of white ashes, as of burnt
paper, an effect produced by the slow action of the air penetrating
through the loose ashes, and which has been impeded or prevented in
Herculaneum by the _tufa_, which, as it were, hermetically sealed
up the town, and prevented any decay, except such as occurs in the
spontaneous decomposition of vegetable substances exposed to the
limited operation of water and air--for instance, peat and Bovey
coal.
Davy ascertained, that what the Neapolitans called varnish,
was decomposed skin that had been used to infold some of the
papyri, and which by chemical changes had produced a brilliant
animal carbonaceous substance, which afforded by distillation a
considerable quantity of ammonia, and left ashes containing much
phosphate of lime.
Only one method, and that a simple and mechanical, though a highly
ingenious one, had been adopted for unrolling the MSS. It was
invented, in the middle of the last century, by Padre Piaggi,
a Roman, and consists in attaching a thin animal membrane, by
a solution of glue, to the back of the MSS. and then carefully
elevating the layers by silk threads, which are gradually moved by
the revolution of wooden pegs. Davy, shortly after his arrival,
desired that the process of unrolling might be continued in his
presence; and in considering the method in its general application,
it occurred to him that some expedient might be used to facilitate
the separation of the layers. For this purpose, he proposed to
mix the solution of glue with a sufficient quantity of alcohol to
gelatinize it, in order that it might not penetrate through three
or four layers, which it was liable to do, when the texture of
the papyrus was loose or broken, and the glue employed was in a
liquid state. He also suggested the application of warm air for
drying the papyrus, in the operation of attaching the membrane. It
is not my intention to follow the chemist through all the various
processes which he instituted for accomplishing his object; they
may, however, be found in his paper entitled "Some Observations and
Experiments on the Papyri found in the Ruins of Herculaneum," which
was read before the Royal Society on the 15th of March 1821, and
published in the Transactions of that year.
It only remains to be stated that Davy was not successful; but
though the process of unrolling hitherto applied may not have
received any considerable improvement from his science, and though
he may not have succeeded in rendering any of the manuscripts
legible, the failure is not to be attributed to his want of zeal,
or to his want of skill, but solely, as it is generally admitted,
to the unfortunate condition of the papyri.
It will be readily supposed that a failure in an investigation,
from which he had anticipated so much advantage, was not sustained
by a person naturally quick and irritable, without some
demonstrations of impatience and dissatisfaction.
It was probably under the influence of such feelings, that he
composed the conclusion of his memoir. "During the two months that
I was actively employed in experiments on the papyri at Naples, I
had succeeded, with the assistance of six of the persons attached
to the Museum, and whom I had engaged for the purpose, in partially
unrolling twenty-three MSS., from which fragments of writing were
obtained, and in examining about one hundred and twenty others,
which afforded no hopes of success; and I should gladly have gone
on with the undertaking, from the mere prospect of a possibility
of discovering some better result, had not the labour, in itself
difficult and unpleasant, been made more so, by the conduct of the
persons at the head of this department in the Museum. At first,
every disposition was shown to promote my researches; for the
papyri remaining unrolled were considered by them as incapable
of affording any thing legible by the former methods, or, to use
their own word, _disperati_; and the efficacy and use of the new
processes were fully allowed by the _Svolgatori_, or unrollers of
the Museum; and I was some time permitted to choose and operate
upon the specimens at my own pleasure. When, however, the Reverend
Peter Elmsley, whose zeal for the promotion of ancient literature
brought him to Naples for the purpose of assisting in the
undertaking, began to examine the fragments unrolled, a jealousy
with regard to his assistance was immediately manifested; and
obstacles, which the kind interference of Sir William A'Court was
not always capable of removing, were soon opposed to the progress
of our enquiries; and these obstacles were so multiplied, and made
so vexatious towards the end of February, that we conceived it
would be both a waste of the public money and a compromise of our
own characters to proceed."
* * * * *
While in Italy, Sir H. Davy visited the baths of Lucca, and
examined the waters which have given to that place so much
celebrity. The results of his analysis formed the subject of a
paper, which was published in the Memoirs of the Royal Academy of
Sciences at Naples, of which Society he was a member.
At the spot where the temperature of the water was the highest,
that is, in what are termed the _Caldi_, or hot baths, a
considerable quantity of a substance is ejected, which produces a
deposit of a brownish-yellow colour. Having collected a quantity
of this deposit, he ascertained it to consist of oxide of iron
and silica, in the proportion of about four parts of the former
to three of the latter; and although the iron, at the time of
its deposition, proved to be a _peroxide_, he thinks it probable
that it existed in the water in the state of _protoxide_. He also
supposes, that the oxide of iron and the silica had been dissolved
together in the water, and been deposited from it in combination.
He conceives that the fact which he had some years before noticed,
of the analogy between the base of silica, and that of boracic
acid, together with those observed by Berzelius, furnish sufficient
reasons for classing silica amongst the acids, and for rendering
it probable, that the oxide of iron and silica undergo a real
chemical combination in the warm water, and that they are separated
from the latter in consequence of the reduction of its temperature,
after it has issued from the mountain.
A small portion of oxide of iron, he observes, is found in the
waters of Bath, in which case it is also accompanied by silica;
and he believes that, in many other instances, the oxide of iron
is dissolved in water through the same agency: he moreover regards
such facts as throwing considerable light upon the manner in which
ochre is generated.
Sir Humphry Davy returned to England in 1820; and, on the 19th of
June, in the same year, his venerable friend Sir Joseph Banks,
who, notwithstanding his increasing infirmities, had continued
to discharge the duties of President of the Royal Society to the
latest period of his life, expired at his villa at Spring Grove, at
the advanced age of seventy-seven.
Discussions necessarily arose as to the appointment of a proper
successor, when persons of high and even exalted rank were proposed
as candidates; but the more influential members of the Society at
once found, in their own Council-chamber, two philosophers, whom
they considered equally entitled to the honour of the situation,
and equally well calculated for the discharge of its duties--Sir
Humphry Davy, and Dr. Wollaston; but the latter having signified
his fixed determination to decline competition, gave the whole
weight of his influence to the former; and, under that arrangement,
he received from the Council the compliment of being placed in
the chair, until the general election of officers at the ensuing
anniversary.
As the period of election approached, a few Fellows of the Society
attempted to raise a clamour in favour of some more aristocratic
candidate. To this circumstance, Davy alludes in the following
letter.
TO THOMAS POOLE, ESQ.
Grosvenor Street, June 1820.
MY DEAR POOLE,
I regret very much that you could not join me at dinner this
day. To-morrow and the following day I shall be occupied
by pressing affairs; but I shall be at home to-morrow till
half-past eleven, and be most happy to see you.
I am not very anxious to remove "mists," for I feel that the
President's chair, after Sir Joseph, will be no light matter;
and unless there is a strong feeling in the majority of the
body that I am the most proper person, I shall not sacrifice my
tranquillity for what cannot add to my reputation, though it
may increase my power of being useful.
I feel it a duty that I owe to the Society to offer myself; but
if they do not feel that they want me, (and the most active
members, I believe, do) I shall not force myself upon them.
I am, my dear Poole, very sincerely yours,
H. DAVY.
On the day of election, (November 30, 1820,) there was a feeble
expression in favour of Lord Colchester, who was abroad at the
time, and had not even been made acquainted with the intention
of his supporters. Davy was therefore elected by an immense
majority of votes. He was conducted into the meeting-room by his
two friends, Mr. Davies Gilbert and Mr. Hatchett, and, to the
gratification of every lover of science, he ascended the chair of
Newton.
The value which he himself attached to this triumph, may be seen in
his answer to a letter of congratulation from his friend Mr. Poole.
TO THOMAS POOLE, ESQ.
Grosvenor Street, Dec. 10.
MY DEAR POOLE,
I am much obliged to you for your congratulations. The contest
to my election defeated itself, for there were only thirteen
votes for Lord Colchester out of nearly one hundred and sixty;
and, had it been known that the attempt would have been made,
I should have had at least double the number. The overwhelming
majority has, however, shown the good opinion of the Society,
which I trust and feel has not been diminished by my conduct in
the chair.
I have never needed any motive to attach me to science, which
I have pursued with equal ardour under all circumstances, for
its own sake, and for the sake of the public, uninfluenced by
the fears of my friends, or the calumnies of my enemies. I
glory in being in the chair of the Royal Society, because I
think it ought to be a reward of scientific labours, and not an
appendage to rank or fortune; and because it will enable me to
be useful in a higher degree in promoting the cause of science.
To this cause, however, I should have been always attached,
even had I not been in such good humour with the public, as I
have reason to be.
Dr. Wollaston, my only formidable opponent in the beginning of
the business, behaved like a true philosopher and friend of
science; and Mr. Gilbert gave me his warmest support.
I am sorry that I have said so much about myself, but
your long letter called for something. I wish I could say
anything satisfactory on the subject of Captain Parry and his
officers.[63] I have every reason to believe Lord Melville
will do all he can on the occasion; no recommendation will
be wanting from the Royal Society that can be given; but the
Admiralty is bound by certain general rules, and will not do
more in this instance than they would do in the case of a
brilliant combat; but these brave and scientific navigators
will be rewarded by a more durable species of glory.
Lady Davy joins me in kind remembrances.
I am, my dear Poole, sincerely yours,
H. DAVY.
[63] Mr. Poole informs me, that he "had been anxious to interest
him, as President of the Royal Society, in favour of those brave
and scientific navigators, particularly Lieutenant, now Captain,
Liddon, who commanded the Griper, in Captain Parry's first
voyage."
It was a question anxiously discussed by the friends of Davy, how
far his elevation to the chair of the Royal Society was calculated
to advance the cause of science, or to increase the lustre of his
own fame. It will be readily perceived that this is a question
perplexed by various conflicting interests, for it not only
involves considerations relating to the character of the person,
but to that also of the constitution and objects of the Society
over which he is called upon to preside.
It is still doubtful whether the Royal Society, in the present
advanced state of science, can derive advantage from possessing in
its President, a philosopher actively engaged in any one branch of
experimental enquiry. Sir Humphry Davy, in his first address from
the chair, took occasion to observe, that "in the early periods of
the establishment, when apparatus was procured with difficulty,
when the greatest philosophers were obliged to labour with their
own hands to frame their instruments, it was found expedient to
keep in the rooms of the Society a collection of all such machines
as were likely to be useful in the progress of experimental
knowledge; and curators and operators were employed, by whom many
capital experiments were made under the eyes of the Society.[64]
But since the improvement of the mechanical and chemical arts
has afforded greater facilities as to the means of carrying on
experimental research, the transactions of the Fellows, recorded
by the Society, have, with some few exceptions, been performed in
their own laboratories, and at their own expense."
[64] The Charter of the Royal Society states that it was
established for the improvement of NATURAL science. This epithet
"_natural_" was originally intended to imply a meaning of
which very few persons, I believe, are aware. At the period of
the establishment of the Society, the arts of witchcraft and
divination were very extensively encouraged; and the word natural
was therefore introduced, in contradistinction to _super_-natural.
Although Sir Walter Scott, in his Demonology, alludes to
the influence of this Society in diminishing the reigning
superstition, he does not appear to have been acquainted with the
circumstance here alluded to.
In deciding upon the qualifications necessary for a President, this
altered state of the Society must not be overlooked; nor can it be
concealed, that the great discoveries of modern science have been
achieved without any direct assistance from the Royal Society. Davy
would have discovered the laws of electro-chemistry, and applied
them for the decomposition of the alkalies--and the genius of
Dalton would, by his atomic doctrine, have "snatched the science
from the chaos of indefinite combination, and have bound it in the
chains of number," had the Society never existed. At the same time,
it must be allowed that, although it may not have directly advanced
the progress of science, it has materially assisted its cause, by
perpetuating the spirit of philosophical enquiry, and the love of
scientific glory--by keeping alive upon the altar the sacred flame
that genius may have kindled.
In the present state of science, the Royal Society imparts an
inspiring principle to its various branches, by affording a
rallying point, a centre of communication, to the philosophers
of all nations, to whom kindred pursuits may render personal
intercourse beneficial; and it becomes the paramount duty of the
chief of this great republic so to preside over its arrangements,
as to foster and encourage such an alliance. To this end, he
must promote feelings of mutual kindness and liberality; and as
the friend and umpire to all parties, it is his office to settle
disagreement, to soothe disappointment, to kindle hope, and to
subdue the vehemence which "engenders strife," in order that
rivalship shall not pass into hostility, nor emulation degenerate
into envy. It is evident that the talents and qualifications
necessary for the discharge of such duties are of the highest
order, extensive in their range, and diversified in their
character. To which, however harshly the word may grate upon the
ear of the philosopher, WEALTH must be considered as an essential
and indispensable condition.
It may be fairly asked, whether a philosopher actively engaged
in the pursuit of any branch of science, is so well adapted
for the performance of such varied duties, as the person who
possesses a general acquaintance with every department, but is not
exclusively devoted to the investigation of any one branch; for,
however correct may be his decisions, or unbiassed his judgment,
the conduct of the former will ever be open to the charge of
partiality, and the bare existence of such a suspicion, though it
may be wholly groundless, will carry with it a train of evils. It
is not in human nature to believe that the looker-on, and he who
plays the game, are alike indifferent to the cards.[65]
[65] I state this opinion with the greater confidence, from a
conviction that it is not singular. On conversing lately upon
the subject with a gentleman to whom the Royal Society is deeply
indebted for the sound judgment and discretion he displayed on
occasions greatly affecting its interests, he replied, "Sir, we
require not an Achilles to fight our battles, but an Agamemnon to
command the Greeks."
On the other hand, it may be urged with some force, that the
Presidency of the Royal Society should be reserved as the fair
reward of scientific labours, and not as an appendage to rank or
to wealth:--that in England, we may in vain search amongst the
aristocracy for one who feels a dignified respect for the sciences,
and who is willing to afford that time which the faithful discharge
of its duties would require.
To assert that Davy retained his popularity, or to deny that he
retired from the office under the frown of a considerable party,
would be dishonest. I would willingly dismiss this part of his life
without too nice an examination; but I am writing a history, not an
eloge.
As a philosopher, his claims to admiration and respect were
allowed in all their latitude; but when he sought for the homage
due to patrician distinction, they were denied with indignation.
How strange it is, that those whom Nature has placed above their
fellow men by the god-like gift of genius, should seek from their
inferiors those distinctions which are generally the rewards
of fortune. When we learn that Congreve, in his interview with
Voltaire, prided himself upon his fashion rather than upon his wit;
that Byron was more vain of his heraldry than of his "Pilgrimage
of Childe Harold;" that Racine pined into an atrophy, because the
monarch passed him without a recognition in the ante-room of the
palace, and that Davy sighed for patrician distinction in the chair
of Newton, we can only lament the weakness from which the choicest
spirits of our nature are not exempt. Will philosophers never feel,
with Walpole, that "a genius transmits more honour by blood than
he can receive?" Had the blood of forty generations of nobility
flowed in the veins of Davy, would his name have commanded higher
homage, or his discoveries have excited greater admiration? But
great minds have ever had their points of weakness: an inordinate
admiration of hereditary rank was the cardinal deformity of Davy's
character; it was the centre from which all his defects radiated,
and continually placed him in false positions; for the man who
rests his claims upon doubtful or ill-defined pretensions, from
a sense of his insecurity, naturally becomes jealous at every
apparent inattention, and he is suspicious of the sincerity of
that respect which he feels may be the fruit of usurpation. If
with these circumstances we take into consideration the existence
of a natural timidity of character, which he sought to conquer by
efforts that betrayed him into awkwardness of manner, and combine
with it an irritability of temperament which occasionally called up
expressions of ill-humour, we at once possess a clue by which we
may unravel the conduct of our philosopher, and the consequences it
brought upon himself during his presidency of the Royal Society.
Nor must we leave out of sight that inattention to certain forms
which, amongst those who are incapable of penetrating beyond
the surface of character, passes for the offensive carelessness
of superiority. Davy, after the example of Sir Joseph Banks,
opened his house on one evening of the week for the reception of
the Fellows of the Royal Society, and of other persons who were
actively engaged in any scientific pursuit; but the invitations to
these _soirées_ were so irregularly managed, that they frequently
gave offence, where they were intended to convey a compliment.
Conflicting opinions, respecting the management of the Royal
Institution, most unfortunately also arose, and the President of
the Royal Society, presuming upon his former alliance with that
establishment, and upon the high obligations conferred upon it
by the splendid discoveries he had achieved within its walls,
was encouraged to exercise an authority which provoked an angry
dissatisfaction;--schisms arose, and the party-spirit thus kindled
in Albemarle Street soon spread to Somerset House.--But let us
turn to the brighter part of the picture. In the discharge of the
more important duties of his office, the Society received the
full benefit of his talents and his virtues. At its meetings,
he was constant in attendance, and dignified in his conduct and
deportment; in its councils, he was firm in his resolves, correct
in his judgments, zealous in his plans,[66] and impartial in his
decisions. It has been said that he unduly favoured the pursuits of
chemistry, to the injury and depression of the other branches of
science: this is not the fact, as a reference to the Philosophical
Transactions will amply testify; and the awards of the Copley
medals will moreover show, that he alike extended the animating
influence of his patronage to every part of natural philosophy.
I am authorised by Sir James South to state, that during his
negotiations with the Government, for the purpose of securing to
the British Nation the unalienable use of his splendid instruments,
by the erection of a permanent observatory, Sir Humphry Davy was
indefatigable in his exertions to accomplish so important an
object; and that on one occasion, in the midst of severe illness,
he travelled at no inconsiderable risk to London, from the distant
seat of his friend Mr. Knight, to advocate a cause so essential, in
his judgment, to the interests of Astronomy.
[66] It was well known to his friends that, had his health not
declined, he would have carried into effect a reform which he
had long contemplated, and by which the Royal Society would have
become, at once, more dignified and more useful.
* * * * *
In the Autumn of 1821, Davy visited his mother and relatives at
Penzance; upon which occasion he received from the inhabitants of
the town, and from the gentlemen resident in its neighbourhood,
a flattering testimony of respect, which made a deep and lasting
impression upon his heart.
At a General Meeting, summoned for the purpose of taking into
consideration some mode by which his fellow-townsmen might express
their sense of his transcendent talents, and of the lustre which
his genius had cast upon the place of his nativity:--It was
unanimously RESOLVED--
"That a public dinner be given to Sir Humphry Davy, and that
the Mayor be desired to wait upon him forthwith, in order to
communicate the Resolution, and respectfully to request that he
would appoint the day, on which it would be agreeable to him to
meet their wishes."
On the day appointed, a deputation of Gentlemen proceeded in
their carriages to the house of his mother, for the purpose of
conducting him to the hotel, where an appropriate entertainment had
been provided for the occasion.
The following letter evinces the sincere satisfaction which this
visit afforded him.
TO THOMAS POOLE, ESQ.
Penzance, July 28, 1821.
MY DEAR POOLE,
An uncontrollable necessity has brought me here. Close to the
Land's-end I am enjoying the majestic in nature, and living
over again the days of my infancy and early youth.
The living beings that act upon me are interesting subjects
for contemplation. Civilization has not yet destroyed in their
minds the semblance of the great Parent of good.
Nature has done much for the inhabitants of Mount's Bay, by
presenting to their senses all things that can awaken in the
mind the emotions of greatness and sublimity. She has placed
them far from cities, and given them forms of visible and
audible beauty.
I am now reviving old associations, and endeavouring to attach
old feelings to a few simple objects.
I am, &c.
H. DAVY.
Although the letter which follows is without date, I am unwilling
to withhold it.
TO THOMAS POOLE, ESQ.
MY DEAR POOLE,
I have been for some weeks absent from London, and have only
just received your letter. When I return in the winter, I shall
be glad to see Mr. A.--I regret that your niece is so much
indisposed. Lady Davy has been obliged to change her climate in
consequence of a long-continued cough, but I am happy in being
able to say she is now quite well.
After the fatigues of a long season in London, I am now
enjoying the Highland scenery and sports with a purer pleasure,
and I find, after the Alps and Pyrenees, even the mountains of
Scotland possessing some peculiar beauties. You ought to come
and see this country, which you would enjoy, both as a lover of
nature and of man. The one is grand and beautiful; the other,
moral, active, and independent.
I am, my dear Poole, your obliged friend,
H. DAVY.
The Philosophical Transactions, during the Presidency of Sir
Humphry Davy, evince the alacrity with which he redeemed the pledge
given to the Society in his address on taking the chair--
"And though your good opinion has, as it were, honoured me with a
rank similar to that of General, I shall be always happy to act as
a private soldier in the ranks of Science."
* * * * *
Many years before even the identity of lightning and electricity
was suspected, it had been observed, on several occasions, that
the magnetism of the compass needle was not only destroyed, which
might have been attributed to heat, but that it was even reversed
by lightning.[67]
[67] Davy observes, that there are many facts recorded in the
Philosophical Transactions, which prove the magnetising powers
of lightning: one in particular, where a stroke of lightning
passing through a box of knives, rendered most of them powerful
magnets.--_Philosophical Transactions_, No. 157, p. 520, and No.
437, p. 57.
In the progress of electrical discoveries, the similarity between
electricity and magnetism had not escaped observation,[68] and
some philosophers had even attempted to establish the existence
of an identity or intimate relation between these two forces.
The experiments of Ritter, however, alone appeared to offer any
confirmation of the supposed analogy; but so obscure was his
language, and so wild and hypothetical his views, that few, if
any, of them were repeated either in France or England, and their
results were for a long time wholly disregarded.
[68] The phenomena of many crystallized minerals which become
electric by heat, and develope opposite electric poles at
their two extremities, offered an analogy so striking to the
polarity of the magnet, that it seemed hardly possible to doubt
a closer connection of the two powers. The developement of a
similar polarity in the Voltaic pile pointed strongly to the
same conclusion; and experiments had even been made with a view
to ascertain whether a pile in a state of excitement might
not manifest a disposition to place itself in the magnetic
meridian.--_Herschel's Discourse_, p. 340.
In a work, entitled "Recherches sur l'identité des Forces Chimiques
et Electriques," published by M. Oersted in the year 1807, the
subject was resumed, and the author advanced the hypothesis,[69]
which twelve years afterwards conducted him to one of the most
important discoveries of the present age, and which has given
origin to a new science, termed ELECTRO-MAGNETISM.[70]
[69] The hypothesis was this:--"In galvanism, the force is more
_latent_ than in electricity, and still more so in magnetism
than in galvanism; it is therefore necessary to try whether
electricity, in its _latent_ state, will not affect the needle."
This passage may be thus explained: When the Voltaic circuit
is interrupted, it possesses opposite electrical poles; and
when continuous, it no longer affects the electrometer, or
the electricity becomes _latent_, which is the condition
theoretically required for the manifestation of its magnetic
action: and the fundamental experiment of Oersted proved that,
under these circumstances, the compass needle was affected.
[70] Mr. Herschel, in speaking of the pertinacity with which
Oersted adhered to the idea of a necessary connection between
electricity and magnetism, observes, that there is something in
it which reminds us of the obstinate adherence of Columbus to his
notion of the necessary existence of the New World.
In the winter of 1819, Professor Oersted, Secretary to the Royal
Society of Copenhagen, published an account of some experiments, in
which the electric current, such as is supposed to pass from the
positive to the negative pole of a Voltaic battery, along a wire
which connects them, caused a magnetic needle near it to deviate
from its natural position, and to assume a new one, the direction
of which was observed to depend upon the relative position of the
needle and the wire.[71]
[71] For this discovery, the President and Council of the Royal
Society adjudged to M. Oersted the medal on Sir Godfrey Copley's
Donation for the year 1820.
It may be necessary to premise, that these experiments were
conducted in a form which had never before suggested itself to the
enquirer; _viz. with the two ends of the pile in communication with
each other_,--a condition which enabled it to discharge itself
freely: this circumstance will, at once, explain the reason of all
preceding failures. It was never before suspected that the electric
current, passing _uninterruptedly_ through a wire, connecting the
two ends of a Voltaic battery, was capable of being manifested
by any effect; the experiments, however, in question furnished
an unequivocal test of its passage by its action on the magnetic
needle; and which may be shortly stated as follows:
The opposite poles of a battery, in full action, were joined by a
metallic wire, which, to avoid circumlocution, has been called the
_uniting conductor_, or the _uniting wire_.
On placing the wire above the magnet and parallel to it, the pole
next the negative end of the battery always moved westward, and
when the wire was placed under the needle, the same pole went
towards the east. If the wire was on the same horizontal plane with
the needle, no declination whatever took place, but the magnet
showed a disposition to move in a vertical direction; the pole next
the negative side of the battery being depressed when the wire was
to the west of it, and elevated when it was placed on the east side.
The extent of the declination occasioned by a battery, depends
upon its power, and the distance of the uniting wire from the
needle. If the apparatus is powerful, and the distance small, the
declination will amount to an angle of forty-five degrees or more;
but this deviation does not give an exact idea of the real effect
which may be produced by galvanism; for the motion of the needle
is counteracted by the magnetism of the Earth. When the influence
of this latter power is destroyed by means of another magnet, the
needle will place itself directly across the connecting wire: so
that the real tendency of a magnet is to stand at right angles to
an electric current. Such phenomena, being wholly at variance with
the laws of simple electrical attraction and repulsion, are only to
be explained upon the supposition that a new energy is generated
by the action of the current of electricity thus brought into
conflict, and which must be identical with, or nearly related to,
magnetism.
It would also appear from the motions of the magnet, when
differently placed with regard to the _uniting wire_, that this
energy circulates, or performs a circular movement around the axis
of the conductor, and thus drives the magnetic pole according to
the direction of the needle with reference to such a current.
This important discovery was no sooner announced to the
philosophical world, than Sir Humphry Davy, with his characteristic
zeal, proceeded to repeat the experiments; and, with his usual
sagacity, so to vary and extend them, as to throw new light upon
this novel department of science. The facts he thus discovered, and
the reasonings founded upon them, were communicated by him to the
Royal Society in three successive memoirs.
THE FIRST, "On the Magnetic Phenomena produced by Electricity," was
read on the 16th of November 1820.
THE SECOND, entitled "Farther Researches on the Magnetic Phenomena
produced by Electricity; with some new Experiments on the
properties of Electrified bodies, in their relations to conducting
powers and Temperature," read July 5th, 1821.
THE THIRD, "On a new Phenomenon of Electro-magnetism," read March
6th, 1823.
The principal experiments communicated in these memoirs were
performed with the battery belonging to the London Institution,[72]
the once powerful apparatus at the Royal Institution having become
old and feeble in his service.
[72] I find from a note addressed to Mr. Pepys, that on the 21st
of June, 1822, Davy worked the two batteries of 1000 plates each
at the London Institution, before the Prince Royal of Denmark.
The experiments were principally electro-magnetic.
The following letter contains an invitation to his friend Mr.
Pepys, to witness his first experiment; a document so far valuable,
as it fixes a date of some importance in the history of discovery.
TO WILLIAM HASLEDINE PEPYS, ESQ.
Grosvenor Street, Oct. 20, 1820.
DEAR PEPYS,
The experiment I wish to show you is no less than the
conversion of electricity into magnetism; but it is a secret as
yet.
I will come to you at twelve on Monday, in the Poultry. If
you will be so good as to order the battery to be charged
to-morrow, it will be ready for us on Monday.
Have you a dipping needle? This, and an air-pump, and the globe
for taking sparks _in vacuo_ by points of charcoal, are all we
shall want.
Perhaps you will invite Dr. Babington, and our worthy friend
Allen.
I will show you the opening of quite a new field of experiment.
Ever yours very sincerely,
H. DAVY.
The discovery of Professor Oersted was limited to the action of
the electric current on needles previously magnetised. Davy
ascertained that the _uniting conductor itself became magnetic_,
during the passage of the electricity through it.[73] It was in
consequence of having observed some anomaly, with respect to the
way in which the uniting wire altered the direction of the magnet,
that he was led to a conjecture which he immediately verified by
a very simple experiment. He threw some iron filings on a paper,
and brought them near the uniting wire, when immediately they
were attracted by the wire, and adhered to it in considerable
quantities, forming a mass round it ten or twelve times the
thickness of the wire: on breaking the communication, they
instantly fell off, proving that the magnetic effect entirely
depended upon the passage of electricity through the wire.
[73] It would appear that M. Arago likewise discovered this fact
at about the same period; but it is evident that the French and
English philosophers arrived at the result independently of each
other; for the experiments which led to it were made by Sir H.
Davy in October 1820; while the September number of the "Annales
de Physique," containing the first account of the Researches of
M. Arago, was not received in London until the 24th of November
in that year; and it may be farther observed, that the numbers of
this journal were very commonly published several months after
the affixed date.
Davy observes, it was easy to imagine that such magnetic effects
could not be exhibited by the electrical wire, without its being
capable of permanently communicating them to steel; and that, in
order to ascertain whether such was the fact, he fastened several
steel needles, in different directions, to the uniting wire, when
those parallel to it were found to act like the wire itself,
while each of those placed across it acquired two poles. Such
as were placed _under_ the wire, the positive end of the battery
being east, had north poles on the south of the wire, and south
poles to the north. The needles _above_ were in the opposite
direction; and this was constantly the case, whatever might be the
inclination of the needle to the wire. On breaking the connexion,
the steel needles, placed _across_ the uniting wire, retained their
magnetism,[74] while those placed _parallel_ to it lost it at the
moment of disunion. The most extraordinary circumstances, however,
connected with these experiments were, first, that _contact_ with
the uniting wire was not found necessary for the production of
the effect,--indeed, it was even produced, though thick glass
intervened; and, secondly, that a needle which had been placed in a
transverse direction to the wire, merely for an instant, was found
as powerful a magnet as one that had been long in communication
with it.
[74] M. Arago also, nearly at the same time, succeeded in
communicating magnetism to the needle; but, at the suggestion
of M. Ampère, it was effected in a different manner. A copper
wire, by being rolled round a solid rod, was twisted into a
spiral, so as to form a _helix_. It was easy, by passing the
wire round the rod, in one direction or the other, to form a
_dextrorsal_ helix, proceeding from the right hand towards the
left, as in the tendrils of many plants; or a _sinistrorsal_,
or left helix, proceeding downwards from the left hand to the
right above the axis. Into the cavity of a spiral thus formed,
connecting the two poles of a battery, a steel needle wrapped
in paper was introduced; and, in order to exclude all influence
of the magnetism of the earth, the conchoidal part of the wire
was kept constantly perpendicular to the magnetic meridian. In a
few minutes the needle had acquired a sufficiently strong dose
of magnetism; and the position of the north and south poles
exactly agreed with M. Ampère's notion, that the electric current
traverses the connecting wire in a direction from the zinc
extremity of the pile to the copper extremity.
The distance to which magnetism is communicated by electricity,
and the fact of its taking place equally through conductors and
non-conductors, are circumstances which, in the opinion of Davy,
are unfavourable to the idea of the identity of electricity and
magnetism.
Davy subsequently ascertained by experiment, that the magnetic
result was proportional to the quantity of electricity passing
through a given space; and this fact led him to believe, that
a wire electrified by the common machine would not occasion a
sensible effect; and this he found to be the case, on placing very
small needles across a fine wire connected with a prime conductor
of a powerful machine and the earth. But as a momentary exposure
in a powerful electrical circuit was sufficient to give permanent
polarity to steel, it appeared equally obvious, that needles placed
transversely to a wire at the time that the electricity of a common
Leyden battery was discharged through it, ought to become magnetic;
and this he found was actually the fact, and according to precisely
the same laws as in the Voltaic circuit; the needle _under_ the
wire, the positive conductor being on the right hand, offering its
north pole to the face of the operator, and the needle _above_,
exhibiting the opposite polarity.
The facility with which experiments are made with the common
Leyden battery, enabled him to ascertain various other important
facts, respecting the communication of magnetism, which it would
be inconsistent with the nature and limits of this work to
particularize. I have merely offered a notice of the more prominent
discoveries communicated by him in his first paper to the Royal
Society, and which he concludes by observing, that "in consequence
of the facts lately developed, a number of curious speculations
cannot fail to present themselves to every philosophical mind;
such as whether the magnetism of the earth may not be owing to its
electricity, and the variation of the needle to the alterations
in the electrical currents of the earth, in consequence of its
motions, internal changes, or its relations to solar heat; and
whether the luminous effects of the auroras at the poles are not
shown, by these new facts, to depend on electricity. This is
evident, that if strong electrical currents be supposed to follow
the apparent course of the sun, the magnetism of the earth ought to
be such as it is found to be."[75]
[75] A very ingenious piece of apparatus was contrived to
illustrate this theory by experiment; but I am uncertain as
to whom the credit of it belongs. It consisted of a globe,
containing metallic wires, arranged in relation to each other
according to the electro-magnetic theory, when, by passing an
electric current in the direction of the ecliptic, the poles
became magnetic.
Davy never overlooked an occasion of applying theory to practice,
and he therefore proposes, upon the principles developed in this
paper, to make powerful magnets, by fixing bars of steel, or
circular pieces of steel, fitted for making horse-shoe magnets,
round the electrical conductors of buildings in elevated and
exposed situations.
His second paper contains an account of experiments instituted
with a view to gain some distinct knowledge on the subject of the
relations of the different conductors to the magnetism produced
by electricity. The results were decisive; but, without entering
minutely into the theory of the subject which they so ably
illustrated, these experiments cannot be clearly described, or
successfully explained. The same observation will apply to the
researches detailed in his third paper, announcing the discovery
of a _new electro-magnetic phenomenon_; for, since they are
inseparably connected with Mr. Faraday's beautiful experiments on
_Magnetic Rotation_, I could scarcely expect to render my analysis
of the memoir sufficiently intelligible, without entering at length
upon that curious subject; I am unwilling, however, to refer the
reader to the original paper in the Transactions, without offering
a remark upon the _phenomenon_, which he says "is the _principal_
object of the paper," but which we might conclude, from the hasty
and imperfect manner in which he dismisses it, to have occupied a
very subordinate place in his estimation. In his anxiety to examine
and describe the rotations produced during this experiment, he
bestows far too little attention upon the more, indeed I might say
the _only_, important phenomenon of the cone of mercury which was
elevated above each of the wires proceeding from the battery; and
which, arising as it evidently did from a repulsive influence,
clearly shows that the presence of electricity establishes between
the particles of matter a repulsive energy, whether that matter
be conducting, or non-conducting in its functions. This law, M.
Ampère subsequently illustrated by a different form of experiment,
and unfairly, as I must think, omitted even to notice Davy's prior
result.
On the 20th of December 1821, Davy communicated to the Royal
Society a memoir "On the Electrical Phenomena exhibited _in vacuo_."
It had been stated by Mr. Walsh, and the opinion had been
subsequently supported by the researches of Mr. Morgan, that the
electrical light was not producible in a perfect Torricellian
vacuum; the latter gentleman also concluded that such a vacuum
prevented the charging of coated glass.
An enquiry of greater importance can scarcely be imagined;
involving in its train several of the most abstruse and difficult
questions of corpuscular philosophy; as, whether electricity be
a subtile fluid, or electrical effect the mere exhibition of the
attractive powers of the particles of bodies; for, if it can be
shown that these effects take place in a perfect vacuum, we shall
advance towards the conclusion, that electrical phenomena depend
upon the agency of an ethereal and transcendental fluid. It was
under such an impression that Davy proceeded to determine, if
possible, "the relations of electricity to space, as nearly void of
matter as it can be made on the surface of the earth."
He was, in the first instance, led to suspect the accuracy of those
conclusions at which Mr. Walsh and Mr. Morgan had arrived, from
considering that, "in the most perfect vacuum which can be obtained
in the Torricellian tube, vapour of mercury, though of extremely
small density, must still always exist." I propose to follow our
philosopher through the paths of this enquiry; and then, with all
the deference due to such high authority, to state the objections
which may be urged against his results.
First, then, as to the results he obtained with quicksilver in
an apparatus simple, but well adapted at once to insure the most
completely attainable vacuum, and to exhibit its capability of
receiving a charge. In all cases where this vacuum was perfect,
he found it to be permeable to electricity, and to be rendered
luminous, either by the common spark, or by the shock from a Leyden
jar; and, moreover, that the coated glass surrounding it became
charged under such circumstances; but the intensity of the light in
these experiments was always in proportion to the temperature, or,
in other words, to the density of the mercurial vapour; and that
at 20° below zero of Fahrenheit, it became so faint as to require
considerable darkness to render it perceptible.
The great brilliancy, on the other hand, of the electrical light
in pure, dense vapour of mercury, was beautifully displayed during
the operation of boiling the metal in an exhausted tube. "In the
formation and condensation of the globules of mercurial vapour, the
electricity produced by the friction of the mercury against the
glass, was discharged through the vapour with sparks so bright as
to be visible in daylight."
The charge likewise communicated to the tinfoil was higher, the
higher the temperature; at 0° Fahrenheit it was extremely feeble.
This, like the phenomenon of the electric light, must, he thinks,
depend upon the different density of the vapour of mercury.
But he was desirous of still farther refining his experiments,
so as to exclude, as far as it was possible, the presence of any
volatile matter; and in this part of the enquiry he displayed,
in a very masterly manner, that happy talent in which he so
far surpassed his contemporaries, of suggesting expedients
and contriving new apparatus in order to vanquish practical
difficulties.
To get rid of a portion of mercurial vapour, he employed a
difficultly fusible amalgam of mercury and tin, which was made to
crystallize by cooling in the tube; but, in this case, the results
were precisely the same as when pure mercury had been used. He then
attempted to make a vacuum above the fusible alloy of bismuth, but
he found it so liable to oxidate and soil the tube, that he soon
renounced farther attempts of this kind. Nothing discouraged, he
determined to try the effects of a comparatively fixed metal in
fusion. By melting freshly cut pieces of grain tin, in a tube made
void after having been filled with hydrogen, and by long-continued
heat and agitation, he obtained a column of fixed metal which
appeared to be entirely free from gas; and yet the vacuum made
above this exhibited the same phenomena as the mercurial vacuum,
except that they were not perceptibly increased by heat: a fact
which Davy must have anticipated, as he attributed the greater
display of electrical light, at high temperatures, to the effect
of increased density of vapour; it is therefore a matter of
surprise that he did not give more importance to the phenomenon.
He made two experiments on electrical and magnetic repulsions and
attractions in the mercurial vacuum, and he found that two balls,
the one of platinum, the other of steel, properly arranged for the
purpose, repelled each other, when the conducting wire to which
they were attached was electrified in the most perfect mercurial
vacuum, as they would have done in the usual cases: and that the
steel globules were as obedient to the magnet as in the air; which
last result, he observes, it was easy to have anticipated.
He also made some comparative experiments, with the view of
ascertaining, whether below the freezing point of water the
diminution of the temperature of the Torricellian vacuum diminished
its power of transmitting electricity, or of being rendered
luminous by it. To about twenty degrees, this appeared to be the
case; but between twenty degrees above, and twenty degrees below
zero, the lowest temperature he could produce by pounded ice and
muriate of lime, it seemed stationary; and, as well as he could
determine, the electrical phenomena were very nearly of the same
intensity as those produced in the vacuum above tin.
"It is evident," he says, "from these general results, that
the light (and probably the heat) generated in electrical
discharges depends _principally_ on some properties or substances
belonging to the ponderable matter through which it passes: but
they prove likewise that space, where there is no appreciable
quantity of this matter, is still capable of exhibiting electric
phenomena--viz. those of attraction and repulsion, &c.: a fact
unquestionably favourable to the idea of the phenomena of
electricity being produced by a highly subtile fluid or fluids, of
which the particles are repulsive with respect to each other, and
attractive of the particles of other matter."
However much we may admire the experimental address displayed in
this paper, we must confess that its results are very far from
being satisfactory. His having assumed, without proof, and even
without examination, the theory that a perfect vacuum cannot be
produced in the Torricellian tube, and made it the foundation of
his reasonings, appears to me to have vitiated all his conclusions.
Mr. Faraday has rendered it extremely probable, that a _limit_
does actually exist to the production of vapour by bodies placed
_in vacuo_,[76] beneath which they are perfectly fixed; and if
this be true, it is evident that, at low temperatures, a perfect
vacuum may be produced in the Torricellian tube; and it is highly
probable that Davy did thus actually produce one in several of his
experiments; especially in those where he found that, by a farther
reduction of temperature, no farther diminution of electrical
effect was perceptible: he had in fact arrived at this limit to
vaporization, and therefore a farther reduction of temperature
could not possibly influence the phenomena. In this point of view,
the electrical light would seem to be _primary_, or independent of
foreign matter.--But though the premises be granted, let the reader
pause before he hastens to any conclusion; for the cloud of mystery
has not been dissipated, it has only changed its place. At the
termination of his paper, Davy indulges in a conjecture subversive
of every conclusion deduced from experiments _in vacuo_. "When the
intense heat," says he, "produced by electricity, and the strong
attractive powers of differently electrified surfaces, and the
rapidity of the changes of state, are considered, it does not seem
at all improbable, that the superficial particles of bodies, which,
when detached by the repulsive power of heat, form vapour, may be
likewise detached by electrical powers, and that they may produce
luminous appearances in a vacuum free from all other matter, by the
annihilation of their opposite electrical states."
[76] "On the Existence of a Limit to Vaporization. By M. Faraday,
F.R.S. Corresponding Member of the Royal Academy of Sciences at
Paris." Phil. Trans. 1826. See also a more recent paper by the
same Philosopher in the first number of the new Journal of the
Royal Institution.
During the course of the enquiry, Davy is led to suppose that air
may exist in mercury, in the same invisible state as it does in
water, that is, distributed through its pores; and that absorption
of air may, therefore, explain the difference of the heights of
the mercury in different barometers. This, it must be confessed,
if true, is a most disheartening fact, as it at once precludes the
possibility of any thing like accuracy in our barometers; but Mr.
Daniell, to whom on all subjects of meteorology we are bound to pay
the greatest deference, differs altogether from our philosopher
upon this point, and he adduces a single observation which he
thinks nearly disproves the supposition. "All fluids," says he,
"which are known to absorb air into their pores, invariably emit
it when the pressure of the atmosphere is removed; but, upon an
extensive examination of large bodies of mercury, variously heated
in the vacuum of an air-pump, I never saw a bubble of air given off
from the surface of the metal." Davy, it must be stated, obtained
a far different result; but an observation of Mr. Daniell explains
the cause of it. "Air," he continues, "will rise from the contact
of the mercury with the glass in which it is contained, in exact
inverse proportion to the care with which it has been filled,
but it _never rises from the surface of the mercury alone_. The
difficulty of properly filling a barometer tube, I attribute to the
attraction between the glass and the air--not to that between the
mercury and the air."[77]
[77] "Meteorological Essays and Observations," p. 363.--See
also Bellani's experiments upon this subject, which are so
satisfactory as to remove every doubt from the subject.
On the 13th of June 1822, a memoir was read before the Royal
Society, "On the state of Water and Aëriform matter in cavities
found in certain Crystals. By Sir Humphry Davy, Bart. P.R.S."
It is generally admitted by Geologists, that the greater number of
the crystalline substances of the mineral kingdom must have been
previously in a liquid state; but different schools have assumed
different causes for their solution; some attributing the effect
principally to the agency of water, others to that of heat.
In the paper under consideration, the author very freely avows
himself as the champion of the latter doctrine.
"When it is considered," says he, "that the solvent power of water
depends upon its temperature, and its deposition of solid matters
upon its change of state or of temperature, and that, being a
gravitating substance, the same quantity must always belong to the
globe, it becomes difficult to allow much weight to the arguments
of the Wernerians, or Neptunists, who have generally neglected, in
their speculations, the laws of chemical attraction.
"There are many circumstances, on the contrary, favourable to that
part of the views of the Huttonians, or Plutonists, relating to the
cause of crystallization; such as the form of the earth, that of
an oblate spheroid flattened at the poles; the facility with which
heat, being a radiating substance, may be lost and dissipated in
free space; and the observations which seem to show the present
existence of a high temperature in the interior of the globe."
He had often, he tells us, in the course of his chemical
researches, looked for facts, or experiments, which might throw
some light on this interesting subject, but without success, till
it occurred to him, as he was considering the state of the fluid
and aëriform matters which are found included in certain crystals,
that these curious phenomena might be examined in a manner to
afford some important arguments as to the formation of the crystal
itself.
Having obtained, through the liberality of his friends, a variety
of appropriate specimens of rock-crystal, he proceeded to submit
them to experiment. Their cavities were opened by means of diamond
drills, under either distilled water, oil, or mercury; the gas was
then expelled from them by the introduction of slender wires, and
the included fluids were drawn out by the aid of fine capillary
tubes.
As soon as an opening was effected, the fluid under which the
operation had been performed rushed into the cavity, and the
globule of elastic fluid contracted so as to appear from six to ten
times less than before the experiment. The fluid was found to be
nearly pure water,--the gas appeared to be azote.
It was an interesting point to ascertain whether the same
circumstances occurred in productions found in rocks which have
been generally considered as of igneous origin, such as the
basaltic rocks in the neighbourhood of Vicenza, the chalcedonies
of which so often afford water. On examining such specimens, when,
to obviate the possibility of any fallacy, they were previously
ascertained to be impermeable to the atmosphere, analogous results
were obtained: water, containing very minute quantities of saline
impregnations, was found to be the fluid, and the gas, as in the
former instances, was ascertained to be azote; but it was in a much
more rarefied state than in the rock-crystals, being between sixty
and seventy times as rare as atmospheric air.
The fact of azote being found in these cavities, he explains, by
supposing that atmospheric air might have been originally included
in the crystals, and that the oxygen had been separated from it by
the attraction of the water; a conjecture which a direct experiment
appeared to confirm.
In reasoning upon the vacuum, or rarefied state of the aëriform
matter in the cavities of rock-crystals and chalcedonies, he very
justly states, that the phenomenon cannot be easily accounted for,
except on the supposition of their having been formed at a higher
temperature than that now belonging to the surface of the globe:
and he thinks it most probable that the water and the silica were
in chemical union, and separated from each other by cooling, since
there are strong grounds for believing that a liquid _hydrate of
silica_ would exist at high temperatures under pressure, and that,
like all liquid bodies in the atmosphere, it would contain small
quantities of atmospheric air. If this be granted, we may readily
explain the phenomena presented by the gaseous and liquid matters
in rock-crystal and chalcedony.
Thus then did Davy assail the Neptunists in their own camp, and
vanquish them with their own weapons; for the fact, which had been
confidently considered by the disciples of Werner, as, above all
others, hostile to the idea of the igneous origin of crystalline
rocks, namely, the existence of water in them, has been made to
afford a decisive argument in favour of the very opinion it had
been brought forward to oppose.[78]
[78] I well remember with what triumph the late Dr. Clarke, in
his popular lectures on Mineralogy at Cambridge, paraded a fine
crystal containing water in its cavity. "Gentlemen," said he,
"there is water enough in the very crystals in my cabinet to
extinguish all the fires of the Plutonists."
In an appendix to the foregoing paper, the examination of two other
crystals is detailed; the results afforded were very different from
those of the preceding ones, but not less favourable to the theory
of igneous origin. One of these crystals was found to contain a
bituminous fluid; on piercing it under distilled water, the water
rushed in, and entirely filled the cavity, so that no aëriform
matter but the vapour of the substance could have been present. The
fact of almost a perfect vacuum existing in a cavity containing an
expansible but difficultly volatile substance, must be considered
as highly favourable to the theory of the igneous origin of
crystals.
In the other crystal, the quantity of aëriform matter was unusually
small in proportion to the quantity of fluid, and from the
peculiarity of its motion, it appeared to be more likely to be
compressed than rarefied elastic fluid; and in piercing the sides
of the cavities, Davy found that this was the case; it enlarged in
volume from ten to twelve times; the fluid was water, but the gas
was too minute in quantity to be examined. There is but one mode of
accounting for this phenomenon. The crystal must have been formed
under an immense weight of atmosphere or fluid, sufficient to
produce a compression much more than adequate to compensate for the
expansive effects of heat.[79]
[79] An explanation which the experiments of Mr. Faraday, on the
condensation of the gases, to be immediately described, will most
fully justify.