Centenary of John Leslie

The article which we reproduce below is The Centenary of Sir John Leslie by Ellice M Horsburgh. It is taken from the University of Edinburgh Journal (Summer 1933), 215-222. The context is described in the first paragraph of the article.

The Centenary of Sir John Leslie (1766 - 1832)

The Edinburgh Mathematical Society celebrated the fame of Sir John Leslie at its opening meeting held in the Mathematical Institute of Edinburgh University on 4th November 1932. Dr Aitken, Past-President, was in the chair. The centenary address, illustrated by lantern slides, was given by Dr E M Horsburgb. There was a large attendance, including representatives of the family. A collection of Leslie relics was on view. The bust by Joseph and the portrait by J Caw after Sir David Wilkie were lent by the University authorities; the Leslie instruments by Professor Barkla and the department of Natural Philosophy; the Leslie books, publications, and letters, by Mr Frank Nicholson and the Library Committee of the University; further letters by the Rev Dr Marjoribanks of Colinton, one of the descendants. A display of personal relics, including the Leslie medals, a copy of the portrait by Henning, one of the caricatures by Kay and a specimen of Leslie's present of the original Wedgwood ware, was shown by Mrs Leslie. The hostesses were Mrs Leslie and Mrs E M Horsburgh.

It was fitting that the meeting in celebration of the centenary of Sir John Leslie should illustrate the material changes of the past century; for modern commerce, which has made our modern world, is founded on the work of the engineer - the modern engine and modern transport. Thus James Watt is the father of what we call modern civilisation. Even in Leslie's day, conditions were almost mediaeval. The railway was only being born at the end of his life. Goods were then transported by pack horse, and by the lumbering wagon, and later by canal boat. Journeys were made on horseback. Wealthy people, demanding speed and luxury, travelled by stage coach sometimes at the thrilling speed of eight miles per hour - not by an airways liner at over one hundred. Sea-borne commerce was carried by bluff-bowed sailing ships which had changed little since the days of the Tudors. The era of the steam boat was just beginning to dawn.

Leslie's native country, which had been exhausted by her wars of independence and her long internal dissensions, was then only beginning to revive. Compared with England her poverty was deplorable. Her resources before the middle of the eighteenth century were almost non-existent. Her engineers, who did so much in modernising Britain and laying the foundation of Britain's commercial power, raised at the same time their own little country to a proud position in the partnership. Leslie was one of the earliest contributors to this great expansion - national, commercial, and scientific.

He was born in Upper Largo, Fife, on 16th April 1766, in a small cottage which was owned by his descendants till the present year, when it was condemned in the great rebuilding scheme which has swept the country. It lay beneath the shadow of the old kirk of Sir Andrew Wood, the famous Scottish admiral of the days of James III and James IV. His mother was Anne Carstairs, who touches history in the Porteous riot. She was one of those present at the entertainment given by Porteous in celebration of his anticipated release.

Leslie was of feeble physique in boyhood, though robust in manhood. He was of strong character which showed at an early age. When four years old he was sent to a school of a sort, kept by an ancient dame, who plied her spinning-wheel in an earth-floored room, while she taught the alphabet to children. Here he sat on a stool by the fireplace, reserved for the youngest and feeblest child. With this seat of honour, forecast of a professorial chair, he was reasonably pleased, but be was at length superseded by an even younger pupil. Indignant at this affront, he hid for a whole day and, when he finally reappeared, he refused absolutely to return to the school. In the neighbouring village of Lundin Mill he received six months' schooling in writing and arithmetic, and his elder brother Alexander gave him some lessons in mathematics. He was then sent to school at Leven, three miles off, where Latin was taught. To Latin he took a violent dislike, of long duration. It will be remembered that Latin - that great relic of the Roman Empire - had been till recently the language of international communication, and was still being used as such in science. Medical students were questioned in Latin in their degree examinations in Edinburgh even during the first quarter of the nineteenth century. The boy was hardly strong enough for the walk to Leven, so, as his hatred of Latin continued, he was withdrawn after six weeks. Such was the amount of school training of the future mathematician and natural philosopher, before entering as a student at the University of St Andrews. But school did not supply all his training, as the kindly minister of Largo lent him some scientific works, when he was about eleven or twelve years old, and urged him to study Latin, adding by way of encouragement that he himself had acquired it in seven years. Leslie retorted that this was a hopeless waste of time. He evidently used his time well, and the self-taught lad must have astonished his elder brother, as he entered St Andrews University at the age of 13, and was found qualified for the senior mathematical class. At the end of the year he gained a prize. He promptly crossed swords with University authorities by refusing to wear a gown. He upheld this by antiquarian research among the charters - and won his point!

His parents must have been hard pressed to maintain him at St Andrews but, in view of his astonishing natural ability, the Chancellor, the Earl of Kinnoull, agreed to defray expenses. But, as he paid the fees, he insisted that Leslie should learn Latin. This argument, known among jocular logicians as "argumentum ad crumenam," is irresistible, and Leslie learnt Latin after all. As a reward he was allowed to attend the class of Natural Philosophy, the great object of his desire. It is interesting to know that he grew to like Latin, and his standard of scholarship was so good that he could enjoy Lucretius. He quoted Latin, and even Greek, copiously in later life.

After six sessions at St Andrews he removed to Edinburgh University, where he studied for three years. Here he met Adam Smith who employed him in tutoring a nephew. Leslie, at this time, gave up an earlier idea of entering the Church and devoted himself to physical science. He continued to be delicate, and was unable for long periods of study, but evidently worked as hard as health permitted. He attained distinction, and was introduced to Mr (later Professor) Playfair. At the age of twenty-two years he published in the Transactions of the Royal Society of Edinburgh his first paper, on the "Resolution of Indeterminate Problems."

But there was little scope then for a young man, although brilliant, who had just left a university. His wants, however, were simple, and he managed to support himself in comfort by his pen and by tutoring little Colin Maclaurin; and he combined these with travel and study. In 1788 he went as tutor to Virginia. In 1790 he tried to push his fortune in London, and about this time, through tutoring, he made friends with the Wedgwoods of pottery fame. He began his construction of instruments about 1794, with his hygrometer and his differential thermometer. He made many investigations in light, heat, and "cold," and the artificial production of ice. Between 1794 and 1799 he toured in Germany, Holland, Switzerland, Denmark, Norway and Sweden. At one time he thought of going to India as a civil engineer. He retired to the Largo cottage and the family circle in 1801-2, to compose his first great work. The primitiveness of this little crowded cottage offers an amazing contrast with the modern subsidising of learning, in palaces, at the cost of millions. The cottage was sufficient for his needs. Here he had collected his apparatus, and he began systematising his papers on heat into his Experimental Inquiry into the Nature and Properties of Heat. Published in 1804, it was dedicated to his friend, M T Wedgwood. It showed great originality and it made him famous. The Royal Society gave him the Rumford Medal.

Twice he had been a candidate for a professorial chair, but had been unsuccessful. In 1805, at the age of 39, he was first favourite for the Professorship of Mathematics in the University of Edinburgh, when his friend Professor Playfair was translated to the chair of Natural Philosophy. Leslie's words descriptive of that famous chair are: "A chair on which the names of the Gregories, of Maclaurin, of Matthew Stewart, and of Playfair, had shed so much lustre."

As a consequence of his candidature there arose an amazing heresy hunt, which raged for a long time. The rival candidate, a minister, Dr Thomas Macknight, was little known to fame, but was backed strongly by the ministers of the Edinburgh Presbytery, who were suspected of endeavouring to secure a monopoly of the Philosophic chairs, and who now accused Leslie of atheism because of a note in his work on heat. Leslie had dared to speak of Hume with approval, stating that he was the first to treat of causation (cause and effect) in a truly philosophical manner, and had remarked that "the unsophisticated notions of mankind are in perfect unison with the deductions of logic, and imply nothing more at bottom in the relation of cause and effect than a constant and invariable sequence." On this the Edinburgh Presbytery charged him with "having laid a foundation for rejecting all the argument that is derived from the works of God, to prove either His Being, or His Attributes." The protest which was tendered by the ministers to the patrons of the chair, then the Provost and Town Council, stated that they were obliged by charter to act with the advice of the ministers. The ministerial attack raged with great violence. Leslie, however, was elected. The controversy still went on, and culminated in a great scene in the General Assembly. Leslie was finally acquitted of atheism at midnight on the second day of the trial, but only by a majority of 12 out of 180. It takes a bulky volume to contain the evidence at the trial and the speeches, but if Leslie had qualified his "cause and effect" by the word physical, the storm would probably have been averted.

Leslie had now found his place. He began at once to re-model the University mathematical courses. Though essentially a physicist, he started to write a complete set of mathematical text-books. He began with geometry, that subject of controversy even in present-day school teaching. Playfair had followed Euclid, but even in 1805 Leslie was a geometry reformer. The prominence which he gives to this subject is so great that his mathematical text-books deal with its branches almost entirely. And yet he disliked and avoided the methods of co-ordinate geometry. He included trigonometry, and no doubt taught other subjects, but he did not place them in his text-books. In 1817 he published The Philosophy of Arithmetic, a very original work, which received high praise.

But his absorbing interests were in Natural Philosophy. In 1810 he had made the great discovery of artificial congelation. It was known that when the atmospheric pressure is reduced, as at a mountain top, the boiling point of water falls. Leslie reduced the pressure by bell-jar and air pump, and removed the water vapour by a vessel of strong sulphuric acid. In this way, as Tait used to say, jocularly, when he showed the experiment, he succeeded in "boiling water into ice." The English scientists were unsuccessful in repeating this experiment, so Leslie went to London and displayed it to the Royal Society in 1811. He published an article thereon in 1813. For this work we may hail him as a pioneer of that vast branch of modern engineering, mechanical refrigeration.

In 1814 he travelled on the Continent, where he found his works better known than in Britain. He met Humboldt, Laplace, and other famous men. Between 1815 and 1824 he wrote largely for the Encyclopaedia Britannica, and also for the famous Edinburgh Review and for many other journals. His information was amazing alike for its minuteness and its extent. In 1819, on the unexpected death of his friend Professor Playfair, Leslie was called to the chair of Natural Philosophy. This was his true position in life.

He devoted himself with enthusiasm to improving the course in Natural Philosophy. He made and collected apparatus for his department. His contemporary, Dr Traill, says of him: "The attraction of his numerous experiments (a novelty), the celebrity of his name, and the opinion entertained of his extraordinary powers, joined with great simplicity and affability of manner, concurred to secure him the respectful homage of his students, and to sustain the glory of the University." This new text-book was to be in three volumes. It marks a period, as the "Thomson and Tait" of its day. The first volume, published in 1823, dealt with the Properties of Matter, and Dynamics, including Hydromechanics. He brought out a second edition in 1829. Occupied with his many other publications, he did not live to complete this course. These pamphlets included the "Progress of Mathematical and Physical Science during the Eighteenth Century," and various contributions to the Edinburgh Philosophical journal - astronomical, meteorological, and physical.

There was a strong practical tendency in Leslie's science. Acquainted as he was with the history of the subject, he knew exactly where to commence his experimental research. Thus he quotes few authorities. He had a strong tendency towards the practical problems of engineering though he professes to write as a pure scientist. He was the first to give a true explanation of capillarity. Probably his most famous student was Thomas Carlyle.

In 1832, on the recommendation of Lord Brougham, then Lord Chancellor, he was created a Knight of the Guelphic Order. He rather despised titles, and preferred "his old distinction as Professor." But he was proud of being elected Corresponding Member of the Royal Institute of France, by thirty-three out of thirty-seven votes.

For long he had enjoyed good health, and had outgrown his early weakness. He was active, though corpulent. While gardening on his small estate of Coates, near Largo, he caught a chill and, neglecting medicine as a thing he had not proved, paid no attention to it, and became dangerously ill. He died in November 1832, in his sixty-seventh year, and was buried in Upper Largo Kirk. He was unmarried. His name is enshrined in the McEwan Hall.

The present branch of the family is descended from his eldest brother Alexander, in five generations to the present day, and with a perfect classical sequence of the names Alexander and James. The nephew of Sir John Leslie was the founder of the well-known Edinburgh firm of civil engineers, Leslie and Reid, which, among its activities, has given to Edinburgh a water supply second to none in the world. The present male representative of the name, Alexander, continues the Leslie tradition of mathematics and engineering.

In character Leslie was simple, good-natured and straightforward, free from jealousy and ready in his appreciation of the work of others. People did not then aim at being all moulded alike, and Leslie was an outstanding individual, well seasoned with good sound prejudices, such as would have delighted Dr Johnson. He must have been somewhat pompous. His style is grandiloquent. To read his books is almost to hear Leslie speak. His vigorous genius valued invention beyond everything. His knowledge was extensive and varied, and striking in its mastery of historical detail. He was held to be "a repository of every known fact in the history of science." Such a person was possible then! Contemporaries spoke of his instruments as exquisite. We can hardly realise now the time and labour this implies in days long before the introduction even of a standard screw-thread. Though sceptical of conclusions in science, he was credulous in ordinary life. Dugald Stewart in venturing to criticise mathematicians says: "Though the mathematician may be prevented in his own pursuits from going far astray by the absurdities into which his errors lead him, he is seldom apt to be revolted by absurd conclusions in other matters. Thus, even in physics, mathematicians have been led to acquiesce in conclusions which appear ludicrous to men of different habits." Physicist though he was, a trace of this was evident in Leslie. He could indulge in unwarranted applications of mathematics, so as to find an analogy between circulating decimals and the lengthened cycles of the seasons; but we may, with the accumulated knowledge of the present year, smile, though not unkindly, at his speculation that the earth was a thin crust filled with light of an overpowering splendour. He believed in the objective existence of cold, and held that the light of the moon was a phosphorescence. But for over 200 years heat was taught to be an imponderable form of matter, and Leslie was not free from this influence. He was, however, on the brink of the discovery of the dynamic interpretation of heat, though he did not succeed in taking the step. This came long afterwards. As regards the phosphorescence of the moon, his small parabolic speculum probably gave no rise of temperature with his differential thermometer at the focus, and the idea of a "cold" light may have led to his opinion. Probably these occasional strange theories arose from his partial deafness. The partly deaf man is afraid to converse, as he always loses the critical words in a conversation. If Leslie could have discussed such theories with his colleagues, he might have modified his views. But partial deafness would prevent that. In one of the letters exhibited by Dr Marjoribanks at the Centenary, Sir Walter Scott, in 18l4, enquires from Leslie - as the master of all scientific knowledge - as to the nature of phosphorescence, for a note in a poem which he is writing - The Lord of the Isles:-

"My dear Sir," (it reads)

" I am going to ask you a great favour - You are aware of the remarkable phenomenon in the northern seas (and elsewhere for what I know) which the sailors call the sea-fire, a sort of flashing phosphoric light arising upon the surface of the waves when disturbed by the course of the vessel or clash of the oars. This I have pressed into my poetical service - but I am anxious to say something of it in a note to those readers who may not have observed this most remarkable appearance and for the materials of such a note I must be indebted to some scientific friend. I know no one to whom I can apply so well as to yourself for such a favour, both as acquainted with all things on heaven and earth and on the waters under the earth, and so capable of describing these mysteries to the uninitiated, and if you can grant me my request I hope you will allow me to point out the source of my information. - Yours very truly, WALTER SCOTT."

Tuesday, 15 November 1814.

In another letter, Leslie disapproves of the vast grants to Babbage for his calculating machines, not, we may be sure, that he objected to calculating machines, but because, as a frugal man, he would object to a waste of money.

Quaint tales are told of Leslie's eccentricities. He was too striking a figure to escape cruel caricature among the Edinburgh worthies. One of his investigations was on the permanency of dye in fibre. For animal fibre he used that nearest at hand, his own hair. It is said that he appeared before his delighted students with patches of his hair all the colours of the rainbow. So great a philosopher must have been a good disciplinarian! A variation of the story is that he was not above vanity, and dyed his hair (to one colour) in his old age to try to improve his appearance. The one tale need not exclude the other. Though he may not have always tended his well-nourished body according to modern hygienic requirements, he was not above ministering to its comfort. On one occasion he is said to have consumed two pounds of almonds and raisins after a good dinner!

An account of Leslie's works will be found among the Notes of the Edinburgh Mathematical Society for the current year.


JOC/EFR April 2007

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