29 o PETER GUTHRIE TAIT 



only to be mentioned here : it will be found in detail in the Reports of the British 

 Association. Every species of inquiry which had to be carried out at Kew : whether 

 it consisted in the testing of Thermometers, Sextants, Pendulums, Aneroids, or 

 Dipping-Needles, the recording of Atmospheric Electricity, the determination of the 

 Freezing-Point of Mercury or the Melting-Point of Paraffin, or the careful study of 

 the peculiarities of the Air-Thermometer: received the benefit of his valuable sug- 

 gestions and was carried out with his scrupulous accuracy. 



About twenty years ago Stewart met with a frightful railway accident, from 

 the effects of which he did not fully recover. He was permanently lamed, and 

 sustained severe injury to his constitution. From the vigorous activity of the prime 

 of life he passed, in a few months, to grey-headed old age. But his characteristic 

 patience was unruffled, and his intellect unimpaired. 



His career as Professor of Physics in the Owens College has been, since his 

 appointment in 1870, brilliantly successful. It has led to the production of an 

 excellent treatise on Practical Physics, in which every necessary detail is given 

 with masterly precision, and which contains (what is even more valuable, and could 

 only have been secured to the world by such a publication) the matured convictions 

 of a thorough experimenter as to the choice of methods for the attack of each 

 special Problem. 



His Elementary Physics, and his Conservation of Energy, are popular works on 

 physics rather than scientific treatises : but his Treatise on Heat is one of the best 

 in any language, a thoroughly scientific work, specially characteristic of the bent 

 of mind of its Author. 



Stewart published, in addition to his Kew Reports, a very large number of 

 scientific memoirs and short papers. Many of these (notably the article in the 

 Encyc. Brit., Qth ed.) deal with Terrestrial Magnetism, in itself as well as in its 

 relations to the Aurora and to solar disturbances. A valuable series of papers, 

 partly his own, partly written in conjunction with De la Rue and Loewy, deals 

 with Solar Physics. His paper on the "Occurrence of Flint Implements in the Drift" 

 (Phil. Mag. I, 1862) seems to have been ignored by the "advanced" geologists, 

 one of whose pet theories it tends to dethrone ; and to have been noticed only by 

 physicists, especially Sir W. Thomson, whose beautiful experiments have done so 

 much to confirm it. His paper on " Internal Radiation in Uniaxal Crystals," to which 

 Stokes alone seems to have paid any attention, shows what Stewart might have 

 done in Mathematical Physics, had he further developed the genuine mathematical 

 power which he exhibited while a student of Kelland's. 



I made Stewart's acquaintance in 1861, when he was the first-appointed Ad- 

 ditional Examiner in Mathematics in the University of Edinburgh, a post which 

 he filled with great distinction for five years. A number of tentative investigations 

 ultimately based upon our ideas as to possible viscosity of the luminiferous medium, 

 effect of gravitation-potential, on the physical properties of matter, etc., led to the 

 publication of papers on " Rotation of a disc in vacuo, Observations with a rigid 

 spectroscope, Solar spots and planetary configurations," etc. These, as well as our 

 joint work called The Unseen Universe, have been very differently estimated by 

 different classes of critics. Of course I cannot myself discuss their value. There is, 



