OBITUARY NOTICE OF BALFOUR STEWART 289 



DR BALFOUR STEWART, F.R.S. 

 (From Nature, Dec. 29, 1887.) 



In the genial Manchester Professor the scientific world has lost not only an 

 excellent teacher of physics but one of its ablest and most original investigators. 

 He was trained according to the best methods of the last generation of experimen- 

 talists, in which scrupulous accuracy was constantly associated with genuine scientific 

 honesty. Men such as he was are never numerous ; but they are the true leaders 

 of scientific progress : directly, by their own contributions ; indirectly, though (with 

 rare exceptions) even more substantially, by handing on to their students the choicest 

 traditions of a past age, mellowed by time and enriched from the experience of the 

 present. The name of Stewart will long be remembered for more than one striking 

 addition to our knowledge, but his patient and reverent spirit will continue to impress 

 for good the minds and the work of all who have come under its influence. 



He was born in Edinburgh, on November ist, 1828, so that he had entered 

 his sixtieth year. He studied for a short time in each of the Universities of St 

 Andrews and Edinburgh, and began practical life in a mercantile office. In the 

 course of a business voyage to Australia his particular taste for physical science 

 developed itself, and his first published papers : " On the adaptation of the eye to 

 different rays," and " On the influence of gravity on the physical condition of the 

 Moon's surface," appeared in the Transactions of the Physical Society of Victoria 

 in 1855. On his return he gave up business for science, and resumed study under 

 Kelland and Forbes, to the latter of whom he soon became Assistant. In this 

 capacity he had much to do with the teaching of Natural Philosophy on occasions 

 when Forbes was temporarily disabled by his broken health. During this period, in 

 1858, Stewart was led to his well-known extension of PreVost's Law of Exchanges, 

 a most remarkable and important contribution to the theory of Radiation. He 

 seems to have been the first even to suggest, from a scientific stand-point, that 

 radiation is not a mere surface phenomenon. With the aid of Forbes' apparatus, 

 then perhaps unequalled in any British University, he fully demonstrated the truth 

 of the conclusions to which he had been led by theory ; and the award of the 

 Rumford Medal by the Royal Society, some years later, showed that his work had 

 been estimated at its true value, at least in the scientific world. In fact his proof 

 of the necessary equality between the radiating and the absorbing powers of every 

 substance (when divested of some of the unnecessary excrescences which often mask 

 the real merit of the earlier writings of a young author) remains to this day the 

 simplest, and therefore the most convincing, that has yet been given. 



Radiant Heat was, justly, one of Professor Forbes' pet subjects, and was there- 

 fore brought very prominently before his Assistant. Another was Meteorology, and 

 to this Stewart devoted himself with such enthusiasm and success that in 1859 he 

 was appointed Director of the Kew Observatory. How, for eleven years, he there 

 maintained and improved upon the memorable labours of Ronalds and Welsh needs 



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