assailant was Faraday himself. Objections, moreover, had been urged by Matteucci, Von Feilitsch and others, on the ground that the experiments had been made with conductors, in which induced currents could be formed, and that the attractions and repulsions observed in the case of diamagnetic bodies were probably due to the interaction between these currents and the magnets brought into play. The challenge was given to produce the so-called polar effects of diamagnetism with nonconductors.

This challenge was accepted. With an apparatus devised by W. Weber and constructed by Leyser of Leipsic, the polarity, which had been previously established in the case of bismuth, was extended by Tyndall to slate, marble, calc-spar, sulphur, and other insulating substances, including the selfsame heavy glass with which Faraday had discovered diamagnetism. The polarity of liquids, both magnetic and diamagnetic, was also established in this investigation.

The literature produced by Professor Tyndall in connection with these researches, consists of a series of memoirs published in the Philosophical Transactions, and since collected in a volume, entitled "Researches on Diamagnetism and Magne-crystallic Action."

In 1856, Professor Tyndall occupied a Friday evening at the Royal Institution with a lecture on the Cleavage of Slate Rocks, following up and developing in the discourse, the observations of Sharpe and Sorby, which connected cleavage with pressure. Professor Huxley, who was present at the lecture, thought that the reasoning which applied to the lamination of slate, might also apply to that of glacier-ice. He and his friend, having already arranged a visit to Switzerland, immediately resolved to associate with this visit an examination of the so-called "ribboned," "veined," or laminated structure of glaciers, which had been brought into special prominence by the researches of Forbes. The present President of the Royal Society, Dr. Hooker, also formed one of the party.

The first clear case in which pressure showed itself as the obvious and undoubted cause of the structure, was observed at the foot of the ice cascade on the Strahl-eck branch of the lower Grindelwald glacier. At the base of the cascade, the surface of the glacier was thrown into violent longitudinal compression, and at right angles to the direction of this pressure, the lamination appeared.

Professor Tyndall pursued this subject in subsequent years. The view had been entertained that the lamination was the mere continuance of the bedding produced upon the heights by successive falls of snow. And though Agassiz had cited an observation of the kind, Professor Tyndall was not satisfied until in 1858, he discovered ice-sections, on which both the bedding and the lamination were plainly exhibited, the one crossing the other at a high angle. A perfect similarity was thus

established between the lamination of glacier-ice and the cleavage of slate rocks.

In 1857, Professor Tyndall, aided by Mr. Hirst, made copious measurements upon the Mer de Glace, and its tributary glaciers. To account for the transformation of snow into ice, and for the apparent viscosity of the glacier, Tyndall invoked the fact of re-gelation discovered by Faraday. The cause of re-gelation has been a topic of discussion in which many able men have taken part.

Thus began Professor Tyndall's yearly visits to the Alps, which have been continued without interruption for one-and-twenty years. Counting his first excursion, in 1849, when he was a student in the University of Marburg, and his difficult winter visit with the view of determining the motion of the Mer de Glace at the close of the inclement December of 1859, Professor Tyndall has made in all three-and-twenty visits to the Swiss peaks and glaciers. His literary productions arising out of these visits are the following:

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Mountain

Various papers in the Philosophical Transactions and elsewhere, including investigations on the physical properties, and molecular structure of lake ice. "Glaciers of the Alps," published in 1860. eering in 1861." "Hours of Exercise in the Alps," and "Forms of Water," a boy's book about glaciers.

Matter presents itself in three forms, the solid, the liquid, and the gaseous. Mainly by the masterly and original researches of Melloni, in connection with which may be mentioned the refined experiments of Knoblauch, the action of solids and liquids upon radiant heat had been amply and beautifully demonstrated. But no similar action of gaseous matters had ever been established. This incompleteness of the field of research attracted Professor Tyndall's attention; it had indeed constituted a subject of conversation between him and his friends some years before he brought his thoughts definitely to bear upon it.

In the early part of 1859, he devised a differential method of experiment, by which the delicacy and severity of the tests previously applied to gases and vapours were indefinitely augmented. Not only were gases. and vapours thus proved competent to act upon radiant heat, but the most astonishing differences in radiative and absorptive power, were proved to exist between them. The difference between mechanical mixtures like air, and chemical combinations like nitrous oxide, in their action upon radiant heat, revealed itself in a very surprising manner.

Professor Tyndall's writings arising out of the researches thus begun, consist of a long series of memoirs contributed to the Philosophical Transactions, and the Philosophical Magazine. They have since been published in a volume, under the title of "Contributions to Molecular

Physics, in the Domain of Radiant Heat," each memoir being preceded by an analysis of its contents.

The leading idea of the entire line of inquiry is to make radiant heat an explorer of molecular condition. The reciprocity of radiation and absorption, dynamic radiation, combustion and incandescence by perfectly non-luminous rays, the action of a planetary atmosphere in raising the planet's temperature, illustrations of the physical cause of transparency, and opacity, and various other points of interest are discussed in these memoirs.

In 1869, Professor Tyndall, while bathing near the Bel Alp, slipped, fell, and was wounded. Through mismanagement erysipelas set in, and the state of his leg and foot for a time was very grave indeed. After six weeks' confinement in bed, under the care of Dr. Gautier, of Geneva, the wound was healed. The Professor remembers with gratitude the kindness of his Geneva friends at that time, and above all that of Lady Emily Peel, in whose beautiful villa on the banks of Lake Leman the cure was completed.

Curiously enough, this very year we find Professor Tyndall engaged in researches intimately connected with the treatment of wounds. He had been working previously at the decomposition of gases and vapours by light, and the formation of what he calls "actinic clouds," as visible results of the decomposition. In their incipient and most highly attenuated state, these clouds, no matter what might be the vapour from which they were formed, showed a pure cerulean blue. Such observations, variously modified and repeated, Professor Tyndall connected with the blue of the sky, and he obtained from his artificial sky all the optical phenomena, those of polarization included, which have been observed in the natural firmament.

In these inquiries it was necessary to employ perfectly moteless air, and this necessity directed Professor Tyndall's attention in a special manner to the floating matter of the atmosphere. His inquiries on this subject led him into the heart of the so-called "germ theory" of putrefaction and infection; and he summed up his views on the subject in a discourse, entitled "Dust and Disease," published in the "Proceedings of the Royal Institution for 1870," and also in Part I. of the last edition of the "Fragments of Science."

The views enunciated in this discourse were received with marked disfavour by the medical profession, with the exception of a few eminent men, the feeling being confirmed, and to all appearance justified, by the subsequent researches of Dr. Bastian. Under conditions never before thought of, even by the most strenuous adherents of the doctrine, this active investigator announced the sure and certain occurrence, in his infusions, of spontaneous generation. According to him, moreover, the swarming life of putrefying wounds, and the microscopic life found in the

blood, tissues, and exudation liquids of animals suffering from acute contagious disease, arise spontaneously within the body. Such a doctrine must materially influence the physician's practice, and must have the most serious bearing upon human life.

Unconvinced of its body, Professor Tyndall, in 1875, commenced an exhaustive examination of the whole subject, from a new point of view. The first instalment of his researches has just been published in the Philosophical Transactions; the result of which may be summed up in the statement, that so far as research has hitherto penetrated, life was never proved to have been produced independently of antecedent life.

To keep congruous things together, we have coupled Professor Tyndall's inquiries of 1869, with those of 1875 and 1876; but other events and investigations, which came between these two dates, must not be omitted.

In the autumn of 1872, the Professor, in response to invitations frequently repeated, went to the United States, and lectured for four months in the principal Eastern cities of the Union. The interest manifested in his lectures was unprecedented. Illustrated reports of them were issued separately by the proprietors of the New York Tribune, and more than a quarter million copies of these reports were sold. The proceeds of the lectures, after travelling and hotel expenses, and the wages of assistants had been deducted, amounted to somewhat over 13,000 dollars, which Professor Tyndall, with an unselfish munificence as unprecedented as the interest shown in his lectures, handed over to trustees to be applied to the perpetual education in the universities of Europe, of two young Americans possessing necessary bias and ability to pursue a scientific life. The fund has been so invested, that its present interest is nearly £200 a year, which, at all events in the Universities of Germany, will suffice for the education of two young men.*

During his stay in America, Professor Tyndall visited Niagara, and he afterwards made his observations on the cataract the subject of a Friday evening discourse, which appears in Part I. of the last edition of his "Fragments of Science."

On his return from America, and in his capacity of scientific adviser to the Trinity House, Professor Tyndall undertook the direction of an investigation, inaugurated by the Elder Brethren, into the causes which affect the transmission of sound through the atmosphere. The inquiry had reference to the establishment of a system of fog-signals upon our coasts. A full report of this difficult and laborious investigation has been placed before the House of Commons; while, in a more con

* A second edition of Prof. Tyndall's American "Lectures on Light," has been published by Messrs. Longman & Co.

densed and organized form, it has been presented to the Royal Society, and published in the Philosophical Transactions.

Every agent to which influence on sound has been hitherto ascribedwind, hail, rain, snow, and fog-was in succession submitted to scrutiny. The result, with regard to the four last-mentioned agents, was a complete reversal of the views generally entertained regarding them. It was proved that none of them exercised any sensible effect on the transmission of sound through the air. The observations made at sea were afterwards verified by experiments in the laboratory, where artificial showers of rain and snow, and artificial clouds and fogs, far heavier and denser than any observed in nature, were proved to be sensibly powerless to stop or stifle sound.

In an investigation, already referred to, Professor Tyndall had operated on visible actinic clouds; in the present inquiry the existence of invisible acoustic clouds, continually drifting through the atmosphere, and rendering it opaque to sound on days of perfect optical transparency, was established. A complete parallelism was proved to exist between those unseen clouds which intercept and scatter the waves of sound, and the clouds of our atmosphere which intercept and scatter the waves of light. In addition to the works already mentioned, Professor Tyndall has published, "Heat, a Mode of Motion;" "Sound;" Lessons in Electricity;" "Notes of a Course of Nine Lectures on Light;" and "Notes of a Course of Seven Lectures on Electrical Phenomena and Theories."

We have thus, as far as our limits allowed, touched upon the various services which Professor Tyndall has rendered to science. Great and admirable as those best qualified for judging know them to be, they become still more worthy of admiration when account is taken of the difficulties with which he has had to contend. It has been mentioned that in early boyhood he did not enjoy the advantages of a good school. It is true this evil was in some degree remedied by his continuance at school till he was nineteen years old; but, on the other hand, he was compelled to devote nearly nine years of the best part of his life to practical work in order to obtain the means necessary for his scientific education. What he has accomplished has been achieved by hard labour, and without external prop or interest of any kind.

In addition

It is satisfactory to know that a life of such self-denying devotedness to science for its own sake has not been without its reward. to the pure delight of searching for scientific truth, Professor Tyndall has reaped a rich harvest of the highest honours. Besides being a Fellow of the Royal Society, he is a member of various foreign scientific societies, a D.C.L. of Oxford, an LL.D. of Cambridge and LL.D. of Edinburgh. His works have been translated and edited by the highest scientific authorities in France and Germany, and the unprecedented success of his lectures in America has been noted above. On the