the late Balfour Steivart. 257 



published their results in three papers, "On the heating of a 

 -disk by rapid rotation in vacuo." {Proc. Roy. Soc, XIV., 

 p. 90 and 339 ; XV., p. 290). 



They have summed up the results of their experiments 

 as follows : — 



r. There is a temporary heat or cold effect which may 

 he supposed to arise in particles very slightly attached to 

 the disk ; this is radiated off chiefly during rotation, and 

 probably does not greatly affect the disk afterwards. 



2. There is a surface gas effect, Avhich in an aluminium, 

 and even in an ebonite disk, is conducted into the interior 

 as it arises, so that it does not greatly radiate during rota- 

 tion of the disk. In a paper disk, however, which is formed 

 ■of a badly conducting material loosely put together, part of 

 the effect does escape as radiation during rotation. 



3. There is a residual effect which is more deeply seated 

 than the gas effect. And in as much as radiation takes 

 place from a perceptible depth, this effect is much more 

 influential than the gas effect in increasing radiation after 

 rotation. In the case of a paper disk, this deeply seated 

 effect will be less diminished by radiation during rotation 

 than the gas effect, and therefore after rotation in such a 

 disk we might expect the gas effect to be peculiarly small. 



During the latter part of Stewart's life his attention was 

 chiefly devoted to meteorology, terrestrial magnetism and 

 solar physics. While at Kew, the important question of 

 accurate temperature measurements presented itself, and 

 rgave rise to a series of experiments on the air thermometer. 

 The results are published in the Transactions of the Royal 

 Society (Pliil Trans., i S6;^). A paper " On the melting point 

 •of Paraffin," published in the Proce-edings of this Society 

 (XII., 1873) originated in the want felt by him of a standard 

 point of temperature between that of freezing and of boiling 

 water. 



The subject of Terrestrial Magnetism is a great loser 



