“No man ever yet made great discoveries in Science who was
not impelled by an abstracted love.”--SIR HUMPHRY DAVY.
At the time when Professor Tyndall was studying at Marburg University,
the principal figure there was Bunsen, who had been appointed Professor
of Chemistry in 1838. He was a profound chemist, and his fame as a
lecturer was so eminent as to attract many foreign students. A prolific
discoverer, and peculiarly happy in his manner of demonstrating his
scientific teaching, he soon fascinated the ardent minds of the two
students from Queenswood. For two years Tyndall attended his chemical
lectures. Indeed he learned German chiefly by listening to Bunsen.
He has himself stated that Bunsen treated him like a brother, giving
his time, space, and appliances, for the benefit of his studies. The
subject which most attracted Tyndall’s attention was electro-chemistry,
upon which Bunsen delivered an admirable course of lectures in 1848.
The whole principle of the voltaic pile was thus explained to him in
a masterful manner. He also made himself acquainted with chemical
analyses, both quantitative and qualitative. He displayed no less zeal
in the study of mathematics. For a considerable period he got private
lessons from Professor Stegmann, under whose tuition he worked through
analytical geometry of two and three dimensions, the Differential and
Integral Calculus, and part of the Calculus of Variations.
His first scientific paper was a mathematical essay on screw surfaces,
respecting which he says:--“Professor Stegmann gave me the subject
of my dissertation when I took my degree: its title in English was,
‘On a Screw Surface with Inclined Generatrix, and on the Conditions
of Equilibrium on such Surfaces.’ I resolved that if I could not,
without the slightest aid accomplish the work from beginning to end it
should not be accomplished at all. Wandering among the pine wood and
pondering the subject, I became more and more master of it; and when
my dissertation was handed in to the Philosophical Faculty it did not
contain a thought that was not my own.”
But the man whose acquaintance at Marburg appeared to exercise most
influence over his career was Dr. Knoblauch, who had just come thither
from Berlin as extraordinary Professor of Physics, and who had already
distinguished himself by his researches in radiant heat. He illustrated
his lectures with a choice collection of apparatus brought from
Berlin; and he not only suggested to Tyndall an exhaustive series of
experiments bearing on a newly-discovered principle of physics, but
supplied him with the necessary apparatus, and placed his own cabinet
at his disposal for that purpose. The subject of investigation was
diamagnetism.
Faraday’s discoveries and experiments in magnetism were then attracting
the attention of the scientific world. He had shown in 1830 that
by moving a magnet within the hollow of a coil of copper wire an
electrical current was produced in the wire. This was a startling and
pregnant discovery. Taking six hundred feet of insulated copper wire
and winding it into a large vertical coil, he arranged the two ends
of the wire into a small coil a little distance away from the large
coil, and immediately above this small coil he suspended a balanced
compass needle by a silk thread. Then, on dropping a bar magnet, or
piece of iron magnetised, into the large coil, the needle, which was
pointing towards the North Pole, instantly swung round, evidently
impelled by magnetic force; when, again, the bar magnet was raised
out of the hollow of the large coil, the needle moved round in the
opposite direction; while it remained motionless so long as the bar
magnet was at rest either inside or outside the coil. It thus appeared
that an electrical current could be produced by the movement of the
bar magnet--by dropping it into the coil or taking it out; and the
current so produced he called an induced current. This operation is
called magneto-electric induction. In 1845 Faraday greatly extended his
magnetic discoveries. He not only established the magnetic condition
of all matter by showing that every known body or thing could be
influenced by magnetism, but he discovered a new property of magnetism,
which he called diamagnetism. This was considered his greatest
discovery.
By suspending bodies of an elongated form between the ends or poles
of powerful magnets, he found that every substance was attracted or
repelled from the magnetic poles; and he divided all bodies into two
great classes, called magnetic and diamagnetic. The way in which a
piece of iron is attracted by the poles or ends of a horseshoe magnet
is a familiar illustration of the action of magnetic bodies, and
the position that such bodies assume, pointing in a line from one
pole to the other, he termed _axial_. On the other hand, diamagnetic
bodies were those which, when freely suspended within the influence
of the magnet, assumed a position at right angles to the line joining
the poles of a magnet, or to the magnetic meridian; in other words,
magnetic bodies pointed axially from pole to pole, or north and south;
while diamagnetic bodies pointed east and west, or in an _equatorial_
direction. Bismuth is a conspicuous example of diamagnetic substances.
Scientific curiosity soon became excited as to the exact nature of the
diamagnetic force in relation to crystals, some of which behaved in a
mysterious manner between the poles of a magnet. Professor Plücker, of
Bonn, discovered that some crystals formed of diamagnetic substances
were not subject to the diamagnetic force; and to account for this
he attributed to crystals an optical axis, upon which the poles of a
magnet exercised a peculiar force. Plücker brought this theory before
the British Association in 1848, and called it a new magnetic action.
At the close of the same year, Faraday told the Royal Society that he
had often been embarrassed by the anomalous magnetic results given by
small cylinders of bismuth, and after investigation he referred these
effects to the crystalline condition of the bismuth. In concluding his
lecture on this subject, Faraday said:--“How rapidly the knowledge of
molecular forces grows upon us, and how strikingly every investigation
tends to develop more and more their importance, and their extreme
attraction as an object of study. A few years ago, magnetism was to
us an occult power affecting only a few bodies: now it is found to
influence all bodies, and to possess the most intimate relations with
electricity, heat, chemical action, light, crystallisation, and,
through it, with the forces concerned in cohesion.” He thought there
was in crystals a directive impelling force distinct from the magnetic
and diamagnetic force.
Frequent conversations on this subject took place between Knoblauch and
Tyndall in Germany during 1849. Knoblauch suggested that Tyndall should
repeat the experiments of Plücker and Faraday; and as this operation
was proceeding they agreed to make a joint inquiry into the deportment
of crystals under the diamagnetic force. They laboured long at the
problem before attaining any encouraging success. They examined the
optical properties of crystals as well as made magnetic experiments
with them, a great many experiments being made without discovering
any new fact. Eventually, however, they found that various crystals
did not act in accordance with the principles enunciated by Plücker,
and the more they worked at the subject the more clearly it appeared
that the deportment of certain bodies under the influence of magnetism
was due, not to the presence of some force previously unknown, but to
the crystalline structure of the substance under investigation, or as
Tyndall put it, to peculiarities of material aggregation. For example,
he showed that while a bar of iron attracted by a magnet sets itself
in a line from pole to pole, an iron bar made of an aggregate of small
bars sets itself in the opposite direction. Tyndall showed that the
cause of the latter bar assuming an equatorial position was simply its
mechanical structure, the small plates composing the “aggregated” bar
setting from pole to pole. He found that the same law regulated the
magnetic deportment of crystals, whose mechanism or structure, however,
was generally less evident.
In 1849 eminent natural philosophers were studying this subject
in England, France, and Germany, and it was expected that the
investigation of diamagnetic phenomena would rapidly throw some new
light upon the molecular forces which determine the conditions of the
material creation. In allusion to this expectation, Tyndall said in
1850, that as nature acts by general laws, to which the terms great
and small are unknown, it cannot be doubted that the modifications of
magnetic force, exhibited by bits of copperas and sugar in the magnetic
field, display themselves on a large scale in the crust of the earth
itself, and as a lump of stratified grit, though a magnetic material,
could be made, on account of its planes of stratification, to act as
if it were diamagnetic, he suggested that this element might have some
influence in determining the varying position of the magnetic poles of
the earth--a subject which still perplexes the scientific world. Not
only has the north magnetic pole gradually been changing its position,
as shown by the records of three centuries, but, according to Barlow,
every place has a magnetic pole and equator of its own; and according
to Faraday the earth is a great magnet, whose power, as estimated by
Gauss, is equal to that which would be conferred if every cubic yard
of it contained six one-pound magnets; the sum of the force being thus
equal to 8,464,000,000,000,000,000,000 such magnets. “The disposition
of this magnetic force is not regular,” said Faraday, “nor are there
any points on the surface which can be properly called poles: still
the regions of polarity are in high north and south latitudes; and
these are connected by lines of magnetic force (being the lines of
direction), which, generally speaking, rise out of the earth in one
(magnetic) hemisphere, and passing in various directions over the
equatorial regions into the other hemisphere, there enter into the
earth to complete the known circuit of power.”
It was in connection with his investigations on this subject that
Prof. Tyndall first saw Prof. Faraday. Returning from Marburg in 1850,
he called at the Royal Institution and sent in his card, together
with a copy of a paper he had prepared, giving the results of his
experiments on magne-crystallic action. Prof. Faraday conversed with
him for half-an-hour, and being then on the point of publishing one of
his papers on magne-crystallic action, he appended to it a flattering
reference to the notes which Tyndall had placed in his hands.
Tyndall went back to Germany, where he worked for another year. In
the beginning of 1851 he went to Berlin, where, he says, Prof. Magnus
had made his name famous by physical researches of all kinds. “On
April 28th, 1851, I first saw this Professor on his own doorstep in
Berlin. His aspect won my immediate regard, which was strengthened to
affection by our subsequent intercourse. He gave me a working place in
his laboratory, and it was there I carried out my investigations on
diamagnetism and magnecrystallic action published in the _Philosophical
Magazine_ for September, 1851. Among the other eminent scientific
men whom I met at Berlin was Ehrenberg, with whom I had various
conversations on microscopic organisms. I also made the acquaintance of
Riess, the foremost exponent of frictional electricity, who more than
once opposed to Faraday’s radicalism his own conservatism as regarded
electric theory. Du Bois-Reymond was there at the time, full of power,
both physical and mental. His fame had been everywhere noised abroad in
connection with his researches on animal electricity. Du Bois-Reymond
became perpetual secretary to the Academy of Sciences, Berlin. From
Professor Magnus, and from Clausius, Wiedemann, and Poggendorff, I
received every mark of kindness, and formed with some of them enduring
friendships. Helmholtz was at this time in Königsberg. He had written
his renowned essay on the “Conservation of Energy,” which I afterward
translated. Helmholtz had, too, just finished his experiments on the
velocity of nervous transmission, proving this velocity, which had
previously been regarded as instantaneous, or, at all events, as equal
to that of electricity, to be, in the nerves of the frog, only 93
ft. a second, or about one-twelfth of the velocity of sound in air
of the ordinary temperature. In his own house I had the honour of an
interview with Humboldt. He rallied me on having contracted the habit
of smoking in Germany, his knowledge on this head being derived from my
little paper on a water-jet, where the noise produced by the rupture
of a film between the wet lips of a smoker is referred to. He gave me
various messages to Faraday, declaring his belief that he (Faraday)
had referred the annual and diurnal variation of the declination of
the magnetic needle to their true cause--the variation of the magnetic
condition of the oxygen of the atmosphere. I was interested to learn
from Humboldt himself that, though so large a portion of his life had
been spent in France, he never published a French essay without having
it first revised by a Frenchman. In those days I not unfrequently
found it necessary to subject myself to a process which I called
depolarisation. My brain, intent on its subjects, used to acquire a
set, resembling the rigid polarity of a steel magnet. It lost the
pliancy needful for free conversation, and to recover this I used to
walk occasionally to Charlottenburg or elsewhere. From my experiences
at that time I derived the notion that hard thinking and fleet talking
do not run together.”
Prof. Tyndall was exceptionally fortunate in getting so easily and so
early into the friendship of such eminent men of science. In those
days to form such eminent acquaintances was no small achievement for
a young Irishman; but on the other hand, he had fully earned this
distinction by the vigour and originality with which he attacked the
latest and most perplexing problem of that time. During the five years
that had elapsed since Faraday discovered diamagnetism, the subject
had been investigated by the greatest scientists in England, France,
and Germany, and no one had done so much to elucidate it as Prof.
Tyndall. In order to master that subject he began in November, 1850, an
investigation of the laws of magnetic attractions. The laws of magnetic
action at distances in comparison with which the thickness of the
magnet vanishes, had long been known, but the laws of magnetic action
at short distances, where the thickness of the magnet comes fully into
play, had not previously been subjected to reliable experiments, and
were therefore at that time a perplexing matter of speculation. That
desideratum he now supplied. He found, among other things, that the
mutual attraction of a magnet and a sphere of soft iron, when both are
separated by a small fixed distance, is directly proportional to the
square of the strength of the magnet, and that the mutual attraction of
a magnet of constant strength and a sphere of soft iron is inversely
proportional to the distance between them.
Next year (1851) he published the results of further investigations
into the relations between magnetism and diamagnetism. He found that
the laws which govern magnetism and diamagnetism are identical, that
the superior attraction or repulsion of a mass in any particular
direction is due to the direction in which the material particles are
arranged most closely together, that the forces exerted are attractive
or repulsive according as the particles are magnetic or diamagnetic,
and that this law is applicable to matter in general.
A paper on “The Polarity of Bismuth,” which might be regarded as a
temporary instalment of his diamagnetic researches, ended with the
remark that during this inquiry he had changed his mind too often to
be over-confident now in the conclusion at which he had arrived. Part
of the time he was a hearty subscriber to the opinion of Faraday that
there existed no proof of diamagnetic polarity; and if, he said, “I now
differ from that great man, it is with an honest wish to be set right,
if through any unconscious bias of my own I have been led either into
errors of reasoning or mis-statements of fact.”
The theory of diamagnetism was still an apple of discord in the
scientific world; and although Prof. Tyndall used the language of
deference rather than of doubt, he did not allow the subject to remain
in a state of uncertainty. He continued his researches in Berlin,
in the private laboratory of Prof. Magnus, who afforded him every
possible facility for carrying on experiments, and took a lively
interest in the investigation. The result was the confirmation of his
previous impression that the action of crystals within the range of a
magnet’s influence (technically called the “magnetic field”) was due
to peculiarities of molecular arrangement. He found, for example, that
a crystal of carbonate of iron, which, when suspended in the magnetic
field, showed a certain deportment, could be pounded into the finest
dust, and the particles could be so put together again that the mass
would exhibit the same deportment as before.
Dr. Bence Jones, the Secretary of the Royal Institution, who had heard
of Tyndall in Berlin in 1851, afterwards invited him to give a Friday
evening lecture at the Royal Institution. “I went,” he says, “not
without fear and trembling, for the Royal Institution was to me a kind
of dragon’s den, where tact and strength would be necessary to save
me from destruction.” The lecture, which was delivered on February
11th, 1853, was “On the Influence of Material Aggregation upon the
Manifestations of Force,” and it gave a beautiful and simple exposition
of the principles of magnetic and diamagnetic action discovered by
himself, the chief being that the line of greatest density is that
of strongest magnetic power. In the course of his lecture he pointed
out that anything which increases density increases magnetic power;
and upon that principle he contended that the local action of the sun
upon the earth’s crust must influence in some degree the diurnal range
of the magnetic needle, which Faraday, on the other hand, attributed
to the modification of our atmosphere by the sun’s rays. While thus
endeavouring to upset Faraday’s theory, he concluded by saying: “This
evening’s discourse is, in some measure, connected with this locality,
and thinking thus, I am led to inquire wherein the true value of a
scientific discovery consists? Not in its immediate results alone, but
in the prospect which it opens to intellectual activity, in the hopes
which it excites, in the vigour which it awakens. The discovery which
led to the results brought before you to-night was of this character.
That magnet was the physical birthplace of these results; and if they
possess any value they are to be regarded as the returning crumbs of
that bread which in 1846 was cast so liberally upon the waters. I
rejoice in the opportunity here afforded me of offering my tribute to
the greatest worker of the age, and of laying some of the blossoms of
that prolific tree which he planted at the feet of the great discoverer
of diamagnetism.” At the conclusion of the lecture Faraday quitted his
usual seat, and crossing the theatre to the corner where the lecturer
stood, cordially shook him by the hand and congratulated him on his
success. A second lecture was delivered by him on June 3rd, 1853,
“On some of the Eruptive Phenomena of Iceland,” and a month later he
was unanimously elected Professor of Natural Philosophy in the Royal
Institution.
Some years previously he had read in a serial publication an account
of Davy’s experiments on radiant heat at the Royal Institution, and
he remembered ever after the longing then excited in him to be able
to do something of the same kind. Now he was to occupy a position
in which he should use, in his own lectures, the same apparatus of
which illustrations were given in the magazine article that had
fired his youthful ambition. To that position he was promoted on the
recommendation of Faraday, and respecting his appointment he himself
said: “I was tempted at the time to go elsewhere, but a strong
attraction drew me here. It was his (Faraday’s) friendship that caused
me to value my position here more highly than any other.”
While the controversy respecting magnetic and diamagnetic hypotheses
was still raging, Faraday delivered a lecture at the Royal Institution
early in 1855 with the express object of cautioning the investigators
of scientific truths against placing too much confidence on any
hypothesis. He stated that every year of increased experience had
taught him more and more to distrust the theories he had once adhered
to; and his present impression with regard to existing Magnetic and
Electrical hypotheses was, that they were very unsatisfactory, and
that the propounders of them had been following in a wrong track. As
an instance of the obstacles which erroneous hypotheses throw in the
way of scientific discovery, he mentioned the unsuccessful attempts
that had been made in this country to educe magnetism from electricity,
until Oersted showed the simple way. He said that the identity of
magnetism and electricity had been strongly impressed upon the minds
of all: when he came to the Royal Institution, as an assistant in the
laboratory, he saw Davy, Wollaston, and Young trying by every way that
suggested itself to them to produce magnetic effects from an electric
current; but, having their minds diverted from the true course by their
existing hypotheses, it did not occur to them to solve the point by
holding a wire, through which an electric current was passing, over a
suspended magnetic needle--the experiment by which Oersted afterwards
proved, by the deflection of the needle, the magnetic property of an
electric current.
Such cautions, however, did not deter Professor Tyndall from defending
the position he had taken up with regard to magnetism and diamagnetism.
He still maintained that the influence of structure was supremely
important,--that under the influence of magnetism or electricity
a normal diamagnetic bar always exhibits a deportment precisely
antithetical to that of a normal magnetic bar; but that, by taking
advantage of structure, it is possible to get diamagnetic bars which
exhibit precisely the same deportment as normal magnetic ones, and
magnetic bars which exhibit a deportment precisely similar to normal
diamagnetic ones. He showed numerous experiments before the British
Association in support of his contention that the diamagnetic force
is a polar one, with a direction opposite to that of the force in
ordinary magnetic bodies. Professor William Thomson, who witnessed
the experiments, certified the success of every one of them; and
stated that Professor Tyndall’s discoveries in this domain of science
had cleared away a mass of rubbish and set things in their true
light, adding that in many cases he had repeated and varied Tyndall’s
experiments, and had found them to be true.
In 1855 he delivered the Bakerian lecture, in which he gave an
elaborate account of his latest researches respecting the phenomena
of diamagnetism. He was now firmly convinced, he said, that the force
that repelled a body was similar in character to that which attracted
a body; in other words, that diamagnetic bodies possess the same kind
of polarity, but in the opposite direction to that of magnetic bodies.
But the opponents of diamagnetic polarity, who were not yet satisfied
by the evidence he adduced, said that his experiments were made with
electrical conductors in which induced currents could be formed that
might account for the attractions and repulsions. Professor Tyndall
thought it would tend to settle the question if he were to use a new
kind of apparatus that would obviate that objection. He therefore
wrote to Professor Weber, of Göttingen, whom Professor William
Thomson described at the time as the most profound and accurate of
all experimenters, asking him to devise more delicate and powerful
means than had hitherto been used in experimental tests. Weber not
only devised a greatly improved apparatus, but had it constructed
under his own superintendence at Leipsig.[2] With this apparatus
Professor Tyndall was able to satisfy the severest conditions proposed
by those who discredited the results of previous experiments. He then
silenced doubt by demonstrating that magnetism and diamagnetism stand,
in respect of polarity, on the same footing, with this difference,
that the one polarity is the inversion of the other. This diamagnetic
polarity, previously established in the case of bismuth, he showed to
exist in slate, marble, calcspar, sulphur, &c. He also established the
polarity of liquids, magnetic and diamagnetic. At the Royal Institution
in February, 1856, he showed that prisms of the same heavy glass as
that with which Faraday discovered the diamagnetic force, behaved
under the magnet in the same way as bismuth; and this evidence was
admitted to be conclusive by the opponents of diamagnetic polarity. The
controversy thereafter subsided.
His chief papers recording his most important investigations in
connection with diamagnetism were afterwards collected into a volume
entitled _Researches on Diamagnetism and Magnecrystallic Action_.
In 1855 Professor Tyndall was appointed Examiner under the Council for
Military Education, and an incident which occurred shortly afterwards
illustrated the confidential relations into which his intimacy with
Faraday had ripened, as well as the independence of character which
distinguished both. Being strongly impressed with the advantage of
increasing the knowledge of physical science given to artillery
officers and engineers, Professor Tyndall advocated a more liberal
recognition of scientific attainments in their examinations. At that
time a committee of the British Association was endeavouring to get
the British Government to recognise the claims of science; and in
reply to inquiries made by that committee as to the expediency of
offering inducements for the acquisition of science and of offering
orders and decorations as rewards for proficiency, Professor Faraday
said: “I cannot say that I have not valued such distinctions; on the
contrary, I esteem them very highly; but I don’t think I have ever
worked for, or sought after, them.” Lord Harrowby, in his address as
President of the British Association, said that the State had till
recently done absolutely nothing for the promotion of science; and
it was remarked as a strange circumstance that though there were
then in the Cabinet the President and President-elect of the British
Association, it was considered too hazardous to apply to the Government
for money for scientific purposes. While this neglect of science was
being freely discussed a number of well-instructed young men were sent
from Trinity College, Dublin, to compete at the Woolwich examinations
in 1856 for appointments in the artillery and engineers, and their
scientific knowledge appeared so creditable that Professor Tyndall
thought it unnecessary to say anything about it. His colleagues, on
the other hand, sent in as usual brief reports with their returns
calling attention to the chief features of the examination, and a
leader in the _Times_ pointed out that the concurrent testimony of the
examiners was that, both in mathematics and classics, the candidates
showed a marked improvement, but that on other points they broke down.
This appeared to Professor Tyndall an unjust reflection upon their
scientific attainments, which were thus ignored. He accordingly wrote
to the _Times_ simply stating that “in justice to the candidates for
commissions in the artillery and engineers examined by me in natural
philosophy and chemistry, you will perhaps permit me to state that the
general level of the answers in the last examination was much higher
than that attained in the first; many of the papers returned to me gave
evidence of rare ability, and if during their future career the authors
of these papers continue to cultivate the powers which they have
shown themselves to possess, they will, I doubt not, justify by their
deeds the high opinion entertained of them.” This modest statement,
intended to put the students right, put himself wrong. The Secretary
of State for War promptly informed him that an examiner appointed by
the Commander-in-Chief had no right to appear in the public papers as
Professor Tyndall had done without the sanction of the War Office.
To this reproof he at once wrote a firm but respectful reply, which,
however, he submitted to Faraday before despatching it. Faraday pointed
out that the consequence of sending such a reply would be dismissal.
Professor Tyndall said he knew that, but he would not silently accept
the reproof of the War Office. “Then send the reply,” said Faraday; and
it was sent. Henceforth Professor Tyndall was in daily expectation of
receiving his discharge. After a delay, the length of which surprised
him, he received a reply, the contents of which still more surprised
him. His explanation was “deemed perfectly satisfactory” by the
Secretary for War, and he therefore continued for many years afterwards
in the service of the Council for Military Education.
One of the next subjects that occupied his attention was the cleavage
of slate rocks. It is a question of great importance in connection with
geological problems, and hitherto only speculative solutions had been
offered of what appeared to be one of the most mysterious but grandest
operations of nature. For twenty years previously geologists were
mostly content to accept on trust the suggestion of Professor Sedgwick,
that crystalline forces had rearranged whole mountain masses so as to
produce a beautiful crystalline cleavage. In 1854 Professor Tyndall
visited the quarries of Cumberland and North Wales, where the question
of cleavage came prominently before him. When at Penrhyn Quarry he was
told that the planes of cleavage were the planes of stratification
lifted up by some convulsion into an almost vertical position. But
a little observation satisfied him that this view was essentially
incorrect; for in certain masses of slate in which the strata were
distinctly marked, the planes of cleavage were at a high angle to the
planes of stratification. A little experiment, he said, demonstrated
that the cleavage of slate was no more a crystalline cleavage than that
of a hayrick. An elaborate examination of all the conditions of the
phenomena led him to the conclusion that cleavage was the result of
pressure, and that this effect of pressure was not confined to slates.
In a lecture delivered in 1856 he stated that for the previous twelve
months the subject had presented itself to him almost daily under one
aspect or another. “I have never,” he said, “eaten a biscuit during
this period in which an intellectual joy has not been superadded to
the more sensual pleasure, for I have remarked in all such cases
cleavage developed in the mass by the rolling-pin of the pastrycook
or confectioner. I have only to break these cakes and to look at the
fracture to see the laminated structure of the mass.” He exhibited some
puff-paste baked under his own superintendence, and explained that
while the cleavage of our hills was accidental, in the pastry it was
intentional.
Among those who heard the lecture upon slaty cleavage was his friend
Professor Huxley, who suggested that probably the principles then
enunciated might account for the structure of glaciers, another subject
that had long perplexed scientific observers. The greatest authority
on glaciers at that time was Professor J. D. Forbes, of Edinburgh
University, who in 1842 declared that a “glacier is an imperfect fluid
or viscous body, which is urged down slopes of a certain inclination
by the mutual pressure of its parts,” and who detected in glaciers a
veined structure which he explained as fissures produced by particles
of ice in motion sliding past each other, leaving the fissures to
be filled with water and to be frozen in winter. On examining the
published observations of Forbes, Professor Tyndall was struck with the
probable accuracy of Professor Huxley’s suggestion, and in order to
examine the matter more thoroughly, the two advocates of the cleavage
theory arranged to visit together the glaciers of Grindelwald, the Aar,
and the Rhone. This personal investigation and subsequent reflection
confirmed Professor Tyndall in his views. He found that glaciers were
formed by the property of ice which Faraday called _regelation_; that
is, the freezing together of two pieces of ice by simple contact and
slight pressure. It is the same property that enables boys to make
snowballs and snow men when the snow is beginning to melt, or when
the warmth of the hand raises its temperature to the point at which
regelation takes place. Professor Tyndall found that when two confluent
glaciers united to form a single trunk, their mutual pressure developed
the veined structure in a striking degree along their line of junction.
In his lectures on the subject at the Royal Institution he ingeniously
illustrated the processes of Nature which make and unmake the glacier.
To show that ice only becomes compressed into a solid mass at a
temperature near that of freezing water, he cooled a mass of ice by
exposing it to the action of the coldest freezing mixture then known.
He then crushed this cooled mass of ice into fragments, and applied
pressure to the fragments for the purpose of making them cohere, but
they did not show the slightest cohesiveness. Very different was their
action when their temperature was raised to the freezing point. When
placed in a wooden cup and pressed by a hollow wooden die a size
smaller than the cup, the pieces of ice became united into a compact
cup of nearly transparent ice. Glaciers, he contended, were formed by
a similar operation. As particles of snow or ice descend the mountain
side, the pressure becomes sufficiently great to compress the particles
into a mass of solid ice, which eventually assumes the magnitude of a
beautiful glacier. He observed that in the laboratory of Nature it was
exactly at the places where squeezing took place that the cleavage of
the ice was most highly developed. In fact, he said, the association
of pressure and lamination was far more distinct in the case of the
glacier than in the case of the slate rock, and as it was now known
that pressure caused the lamination of slate rock, he contended that it
was the same cause that produced like effects in glaciers.
In a lecture delivered early in 1858, he gave an account of some
beautiful phenomena of the glacier. In the preceding September and
October he examined the effect of sending a beam of radiant heat
through a mass of ice. When sunbeams condensed by a lens were sent
through slabs of ice, the path of the beam was instantly studded with
lustrous spots like brilliant stars, and “around each the ice was so
liquefied as to form a beautiful flower-shaped figure, possessing six
petals. From this number there was no deviation. At first the edges
of the liquid leaves were clearly defined: but a continuance of the
action usually caused the edges to become serrated like those of ferns.
When the ice was caused to move across the beam, or the reverse, the
sudden generation and crowding together of these liquid flowers, with
their central spots shining with more than metallic brilliancy, was
exceedingly beautiful.” By means of the electric light and a piece
of ice prepared for the purpose he was able to exhibit these lovely
ice-flowers to a delighted audience at the Royal Institution.
During the years 1857 and 1858 Professor Tyndall continued his
observations of glacier phenomena amid the solitude of the Alps. In
the summer of the latter year he betook himself to the mountains with
the view of settling once for all “the rival claims of the only two
theories, which then deserved serious attention, namely, those of
pressure and of stratification.” Again his former views were completely
confirmed. It is difficult, he said, to convey in words the force of
the evidence which the glacier of Grindelwald presents to the mind of
the observer who sees it; it looked like a grand laboratory experiment
made by Nature herself with special reference to the point in question.
The squeezing of the mass, its yielding to the force brought to bear
upon it, its wrinkling and scaling off, and the appearance of the veins
at the exact point where the pressure began to manifest itself, left no
doubt on his mind that pressure and structure stood to each other in
the relation of cause and effect.
The conclusions at which he arrived as to the structure and movement
of glaciers brought him into collision with Professor Forbes,
whose views, enunciated fifteen years previously, were then widely
accepted as the most scientific exposition of the subject. Forbes
seemed rather sensitive about his own theory, and complained that
he had to some extent been misrepresented. But in the conflict of
opinions Professor Tyndall invariably referred to Professor Forbes’s
labours in connection with the subject in the most appreciative and
complimentary language. For instance, in 1858 he said he would not
content himself with saying that the book of Professor Forbes was the
best that had been written upon the subject; “the qualities of mind,
and the physical culture invested in that excellent work, were such as
to make it, in the estimation of the physical investigator at least,
outweigh all other books upon the subject taken together.” That is more
generous language than Professor Forbes ever used respecting Professor
Tyndall. In 1865, after the heat of controversy had been dissipated,
Forbes wrote that “Dr. Tyndall’s so-called proofs that it is through
‘fracture and regelation’ that a glacier moulds itself to its bed
are to my mind no proofs at all;” and that he regarded Mr. Hopkins’s
mathematical demonstrations about glaciers as “irrelevant mathematical
exercitations.” Nevertheless, Professor Tait, the friend and scientific
biographer of Forbes, said in 1873: “To say that Forbes thoroughly
explained the behaviour of glaciers would be an exaggeration; but he
must be allowed the great credit of being the Copernicus or Kepler of
this science.” As the subject still continues to exercise the intellect
of the scientific explorers of the Alps, suffice it for the present
to say that if time ratifies the position which Professor Tait has
assigned to Professor Forbes, his greatest and boldest successor in the
same field may be described as the Newton of glacier phenomena.
FOOTNOTES:
[2] The force of diamagnetism is vastly feebler than
that of ordinary magnetism. According to Weber,
the magnetism of a thin bar of iron exceeds the
diamagnetism of an equal mass of bismuth about two and
a-half million times.