W. H. Miller, T. C. Hope, J. Leslie 131 



was at first believed to be a carbonate of barium. Dr. Craw- 

 ford threw doubt on this, and suggested that it contained a 

 new substance, and this was confirmed and definitely proved 

 by Hope. 



John Playfair's successor in the Chair of Mathematics at 

 Edinburgh, and subsequently in that of Natural Philosophy, 

 was John Leslie (1766-1832). After passing through the 

 University as a student of Mathematics and then of Divinity, 

 he spent a year as private tutor in Virginia, and subsequently 

 in the family of Josiah Wedgwood, where he devoted his 

 leisure to Natural Science, translating Buffon's " Natural 

 History of Birds." Returning to his native place, Largo, 

 in Fifeshire, Leslie devoted ten years to scientific research, 

 and then settled down at Edinburgh University. He received 

 the honour of knighthood shortly before his death. Leslie's 

 name is generally connected with his researches on radiation, 

 which would have been more fruitful had he been less 

 dogmatic in upholding what he conceived to be Newton's 

 teaching. He refused to recognize the obvious bearing of 

 Herschel's discovery of radiations less refrangible than red 

 light, and formed artificial and erroneous theories to 

 explain the facts. Nevertheless, his experiments on the 

 radiative power of different substances were conducted with 

 great skill and are of permanent value. The differential 

 thermometer, he employed, maintained for a long time its 

 reputation as a delicate and trustworthy instrument. We 

 owe to him also a valuable method of determining the specific 

 heats of bodies by measuring their rate of cooling. He was 

 the first to freeze water by evaporating it rapidly under the 

 action of an air pump, the vacuum being maintained by 

 sulphuric acid, which rapidly absorbed the aqueous vapour 

 formed. He was also the first to give the correct explanation 

 of the rise of liquids in capillary tubes. 



David Brewster (1781-1868), a man of forceful character 

 and great ability, enjoyed a considerable reputation among 

 his contemporaries, but the weight of his influence was not 

 always placed in the right scale. Like Leslie, he adhered 

 to a verbal interpretation of Newton's doctrine, and in 

 face of the rapidly growing and decisive evidence in favour 

 of the undulatory theory of light, his attitude exceeded all 



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