418 SIR JOHN LESLIE.
regarding radiant heat, and the connexion between light and heat, we are un- able to say. But his Differential Thermometer one of the most beautiful and delicate instruments that inductive genius ever contrived as a help to experimen- tal inquiry, and which rewarded its author by its happy ministry to the success of some of his finest experiments must have been invented before the year 1800, as it was described in Nicholson's Philosophical Journal some time dur ing that year. The results of those fine inquiries, in which he was so much aided by this exquisite instrument, were published to the world in 1804, in his celebrated " Essay on the Nature and Propagation of Heat." ' The experimental devices and remarkable discoveries which distinguish this publication, far more than atone for its great defects of method, its very questionable theories, and its transgressions against that simplicity of style which its aspiring author rather r.pui'ned than was unable to exemplify ; but which must be allowed to be a quality j>eculiarly indispensable to the communication of scientific knowledge. The work was honoured, in the following year, by the unanimous adjudication to its author, by the council of the Royal Society, of the Rumford Medals, appropri- ated to reward discoveries in that province, whose nature and limits he had so much illustrated and extended.
Mr Leslie thus distinguished himself by his acquirements, when, early in 1805, in consequence of the translation of pi-ofessor Playfair from the chair of mathematics to that of natural philosophy in the university of Edinburgh, the former became vacant, and the subject of this memoir appeared as a candidate for the situation. It might have been expected that, where the qualifications of the individual were so decidedly above all rivalry, there could have been no hesitation in his native country to confer upon him the honour which he sought Such there might not have been, if what is called the moderate party in the Scottish church, had not been inspired by a jealousy of his liberal principles in politics, accompanied by a desire of advancing one of their own number, to op- pose his election. The person brought forward as the rival candidate was Dr Thomas Macknight, one of the ministers of the city, and son of the venerable commentator on the Epistles, a gentleman highly qualified, no doubt, not only for this, but for almost any other chair in the university ; but who, neverthe- less, could not be matched against an individual so distinguished for the benefits he had conferred on science as Mr Leslie ; and who was moreover liable to the disqualifying consideration that he was already engaged in an office which, to be well done, requires the whole man, while Mr Leslie stood in the light of a most useful member of society in a great measure unprovided for.
The electors in this case were the magistrates and town-council of Edinburgh, and to them Mr Leslie was recommended not only by fame, but by the warmest testimonials from Sir Joseph Banks, Mr Dempster of Dunnichen, Dr Hutton of- Woolwich, Baron Masseres, and Dr Maskelyne. In the supposition that these men were disposed to discharge their trust with fidelity, they could have no hesir tation in preferring Mr Leslie ; and it is to be related to their credit, that they had no such hesitation. On learning the bent of their resolution, the ministers of Edinburgh held various private meetings, as if to indicate the more pointedly that they had a peculiar interest of their own in the matter ; and it was resohed to oppose Mr Leslie's election on the grounds of what they deemed an infidel note in his essay on heat ; employing for this purpose a clause in the funda- mental charter of the college, directing the magistrates to take the advice of the Edinburgh clergy in the election of professors.
1 Previous to this period, Mr Leslie, when not otherwise or elsewhere engaged, used to live with his brothers at Largo ; and there were the experiments for his essay on heat carried on, and the book written.