The chief characteristic of his mind in those days, was its power of visualising the relations of space. He could mentally draw the lines necessary for the solution of complex problems in plane geometry, and could reason upon his mental image as if it had been a diagram drawn on paper. This power of mental presentation enabled him when reading solid geometry to dispense with the models required by all the other members of the class. How important a part it has played throughout the whole of Professor Tyndall's career is strikingly obvious to even a cursory reader of his popular lectures, but can be fully understood only by those who are qualified to estimate the value of his various contributions to science.

In April, 1839, Tyndall left school to join a division of the Ordnance Survey of Ireland, then under the command of Lieutenant George Wynne (one of the Wynnes of Hazlewood) of the Royal Engineers. General Wynne is now one of Professor Tyndall's oldest and most intimate friends. To this sagacious and high-minded gentleman the subject of our memoir is indebted for many acts of kindness which had a direct bearing on his career. One instance of thoughtful generosity deserves special mention. In 1850, when Tyndall came over from Germany to England, on a temporary visit, his friend, General Wynne, naturally supposing his exchequer was low, offered to place his purse at the disposal of his former assistant. The generous offer, so honourable to both parties, was not accepted, because not needed; but it has left an impression upon the Professor's mind that never has been or can be effaced.

Another instance of this kind connected with a friendship which has probably struck its roots more deeply than any other into Tyndall's life, may be noted here. When a youth of scarcely sixteen, Professor Hirst, the present Director of Studies at the Royal Naval College, Greenwich, entered as an articled pupil the office in which Tyndall was then engaged. Separated in age by an interval of nearly ten years, they nevertheless became very intimate, both teacher and pupil finding a common intellectual pasture in the writings of Carlyle. After Tyndall's severance from the railway world, his young friend visited him at Marburg, in 1849. The death of Hirst's nearest relative called him home, at the same time making him the possessor of a small patrimony. This he set his heart on dividing into halves, one of which he pressed on the acceptance of his friend, and he was sorely disappointed to find that friend inflexible in his adherence to his vow of poverty. To some extent, however, the youth had his way; for one morning, while Tyndall was at work in his garret upon the Ketzerbach in Marburg, the postman brought him a closelypacked, heavily-sealed roll, which, on being opened, was found to contain coins, swept from every kingdom and principality in Germany, louis d'ors, thalers, gulden, silber-groschen, kreuzer, and pfennige. In this way,

through a German banker, did the young man contrive to throw £20 into his friend's exchequer. Abandoning the profession chosen for him, when his articles were completed, Mr. Hirst accompanied Tyndall on his return to Marburg in 1850. Here Hirst studied for a considerable time, and afterwards completed his mathematical education in Berlin, Paris, and Rome. For thirty years, without a moment's solution of continuity, a friendship deeper than brotherhood has united these two men.

To return to 1839. Tyndall joined the Ordnance Survey in the capacity of draughtsman, and after having acquired considerable proficiency in laying down maps and lines of triangulation to scale, he was permitted to master the details of field-work. This accomplished, he was allowed to take part in the surveying and mapping of a large and intricate town.

His acquaintance with trigonometrical observation began in this way: a dearth of observers occurring when some observations were needed, he. offered his services, and after some hesitation on account of his want of experience in such work, was entrusted with a theodolite. Taking the instrument into an open field, he studied its parts, mastered their uses, and made the observations, which, on being compared with the results of the triangulation, previously made on a larger scale, were found to be correct. He also mastered all the details necessary for the calculation of heights and areas, both from the measurements of the field-book and from scale and paper. In short, when he quitted the Survey, in 1843, he was practically acquainted with all its processes.

Nearly five years of Professor Tyndall's life were devoted to work of the character sketched above. In 1844, his prospects in this country being the reverse of brilliant, he resolved to go to America, and a portion of his outfit was actually purchased at the time. The project was opposed by some of his most intimate friends, and the sudden outburst of activity in the construction of railways, together with their remonstrances, detained him in this country.

Removing to Halifax, he lived in the midst of the stormy contests between the West Riding Union and West Riding Junction Railways. The stress at this time upon both brain and muscle was very great. It is, perhaps, worth remarking, that Sir John Hawkshaw, Professor Tyndall's successor in the presidential chair of the British Association, was then engineer-in-chief of the Manchester and Leeds Railway, and as such was considered a kind of potentate by young aspirants in Tyndall's position. In Sir John Hawkshaw's office, at Manchester, a few of the later days of Tyndall's railway labours were spent.

But the fierce energy of the time could not last long. Railway enterprise soon became curtailed in its proportions, and the prospects of young engineers suffered accordingly. Self-improvement was the main object of Tyndall's life, and with a view to this he accepted in 1847 the offer of an appointment as teacher at Queenwood College,

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Hampshire, a fine edifice built in a healthy position by the well-known socialist reformer, Robert Owen and his disciples, and called by them Harmony Hall. It was surrounded by large farms, where lessons in the subjects with which Tyndall's labours had rendered him conversant, were given to the more advanced students.

The teacher of chemistry at Queenwood in those days was Dr. Frankland, in whose laboratory Tyndall spent part of his time, relinquishing for this privilege a portion of his salary. Both young men began at length to feel the need of more thorough scientific culture. Tyndall was now in possession of two or three hundred pounds, and having only this to depend upon, he proceeded with Professor Frankland to the university of Marburg, in the province of Hesse-Cassel, Germany. Here in the laboratory of the illustrious Bunsen he pursued his chemical studies, making himself practically acquainted with analytical processes, both qualitative and quantitative.

But Bunsen was much more than a chemist. His knowledge as a physicist was profound, and his celebrated investigations on gas-analysis touch equally the domains of physics and chemistry. For two successive years Tyndall was a regular attendant at his admirable course of chemical lectures. But what most fascinated the student was a course on electro-chemistry, in which the whole subject of Voltaic-electricity was unfolded in the most masterly manner. To no living man is Professor Tyndall so deeply indebted as to his illustrious friend and teacher Bunsen, who generously lavished his time, his space, and his appliances on promoting the interest of his pupil.

In addition to these chemical and physical studies, which most people would think sufficient occupation in themselves, Tyndall worked hard at mathematics during his stay at Marburg, getting up at five o'clock through three long and severe winters. He was fortunate enough to secure for a considerable period private lessons from Professor Stegmann, and worked through analysis, analytical geometry of two and three dimensions, the Differential and Integral Calculus, and partly through the Calculus of Variations.

In physics, which he finally chose as the field of his special studies and original labours, his first teacher was Professor Gerling. But the main influence brought to bear upon him in connection with these studies was his alliance with Dr. Knoblauch, who at that time was called to Marburg as extraordinary Professor of Physics. He brought with him from Berlin a choice private collection of apparatus, with which he illustrated his lectures. Professor Tyndall's researches in radiant heat, though carried out long after his return from Germany, were probably prompted by the experiments of Knoblauch, who had distinguished himself in this field of inquiry before going to Marburg.

Tyndall's first scientific paper was a mathematical essay on screw

surfaces, accepted by the faculty in Marburg as his inaugural dissertation when he took his degree. His first physical paper was a brief one on the phenomena of a water jet, published in the Philosophical Magazine.

Faraday's discovery of diamagnetism, and Plücker's researches on the action of magnetism upon crystals, then attracted universal attention. At the suggestion of Professor Knoblauch, Tyndall commenced an exhaustive investigation of this subject, the two friends agreeing to make the inquiry a joint one. The first brief paper on this subject was published in the Philosophical Magazine for March, 1850. It was followed by a much more elaborate memoir in July of the same year, showing that Plücker's and Faraday's results were due not to the action of any new "optic-axis force," or "magne-crystallic force," but to striking modifications of the known forces of magnetism and diamagnetism by crystalline structure. Tyndall subsequently conducted in Professor Knoblauch's cabinet a long inquiry into electro-magnetic attractions.

Early in 1851 he went to Berlin, where he made the acquaintance of many illustrious men, including Dove, Riess, the two Roses, Mitscherlich, Poggendoff, Clausius, and Du Bois-Raymond. He also had an interview with Humboldt. But his recollections of Berlin are chiefly connected with the late Professor Magnus. Few have done more than this distinguished man to further the efforts of young original workers in physics and chemistry. Besides the apparatus placed by the Prussian Government under his immediate direction, he was ever ready to devote his private means to the promotion of scientific work. In his laboratory Tyndall pursued his researches in diamagnetism and magne-crystallic action, publishing an account of these labours in the Philosophical Magazine for September, 1851.

In that year he returned to England, and resumed for a time his old duties at Queenwood College. Immediately on his return he attended the meeting of the British Association at Ipswich, under the presidency of the Astronomer Royal. He travelled to Ipswich in company with Professor Huxley, and then began a friendship which has remained unbroken for more than five-and-twenty years. A curious circumstance in connection with this event is thus mentioned in Tyndall's work, entitled "Faraday as a Discoverer," p. 204 :

Then, for the first time, and on my way to the meeting of the British Association, I met a man who has since made his mark upon the intellect of his time; who has long been, and who by the strong law of natural affinity must continue to be, a brother to me. We were both without definite outlook at the time, needing proper work, and only anxious to have it to perform. The chairs of Natural History and of Physics being advertized as vacant in the University of Toronto; we applied for them, he for the one, I for the other: but, possibly guided by a prophetic instinct, the University authorities declined having anything to do with either of us. If I remember rightly, we were equally unlucky elsewhere."

At this Ipswich meeting Professor Tyndall had the privilege of renewing the acquaintance, made a year before, with Professor Faraday, and then, it may be said, began another friendship, which ended only with Faraday's death, in 1867.

Professor Tyndall's connection with the Royal Institution arose out of a visit of Dr. Bence Jones, to Berlin, after Tyndall had left that city. In consequence of what he heard of Tyndall from the scientific men of Berlin, he invited him to give one of the Friday evening lectures at the Institution. The circumstance is thus related in the work from which we have just quoted, p. 126:

" In December, 1851, after I had quitted Germany, Dr. Bence Jones went to the Prussian capital to see the celebrated experiments of Du Bois-Raymond; and influenced, I suppose, by what he heard, he afterwards invited me to give a Friday evening discourse at the Royal Institution. I consented, 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. On February 11th, 1853, the discourse was given, and it ended happily. I allude to these things that I may mention that though my aim and object in that lecture was to subvert the notions botn of Faraday and Plücker, and to establish in opposition to their views what I regarded as the truth, it was very far from producing in Faraday either enmity or anger. At the conclusion of the lecture, he quitted his accustomed seat, crossed the theatre to the corner into which I had shrunk, shook me by the hand, and brought me back to the table."

Immediately afterwards, the Chair of Natural Philosophy in the Institution was offered to him. Proposals from other quarters were made at the same time; but the thought of being near Faraday at once determined Tyndall's choice. He was unanimously elected to the post named above in May, 1853.

At this time one of the principal points of discussion among scientific men was, whether the new force of diamagnetism recently discovered, illustrated, and developed with such extraordinary ardour by Faraday, was a polar force, like that of magnetism, or not. On this question Tyndall had contributed a brief paper to the Philosophical Magazine before he quitted Hampshire. In the Royal Institution he now followed up his researches, and the Philosophical Transactions for 1855 contain a memoir in which all the phenomena forming the basis of the prevalent notion with regard to magnetic polarity were shown to have each its exact counterpart in the phenomena of diamagnetism. This investigation placed it beyond doubt that, as regards polarity, magnetism and diamagnetism stand exactly on the same footing, the only difference between them being, that the one polarity is an inversion of the other. The most celebrated supporter of diamagnetic polarity in those days was Professor Weber of Göttingen; while by far its most celebrated