228 Sir John Conroy. On the Refractive Index of [June 20, 



identify the inertia of matter with, the electric inertia of the electrons, 

 if only we may assume their nuclei to be small enough, or sufficiently 

 numerous. And the fact that these nuclei have free periods of elastic 

 radial vibration in the fluid asther, not subject to damping by radia- 

 tion, reminds us that a pulsatory theory of gravitation has been 

 developed by Hicks and Bjerknes. There is no recognised funda- 

 mental interaction of electric and radiative phenomena with gravita- 

 tion, so for present purposes we are not bound to produce a precise 

 explanation of gravitation at all. The scope of this remark is 

 restiicted to merely showing that a rotational aether is not 'incom- 

 petent to include such an action among its properties. 



III. "On the Refractive Index of Water at Temperatures 

 between and 10." By Sir JOHN CONROY, Bart., F.R.S., 

 Fellow and Bedford Lecturer of Balliol College, and Millard 

 Lecturer of Trinity College, Oxford. Received May 16, 

 1895. 



In 1856 Jamin (' Comptes Rendus,' vol. xliii, p. 1191) published 

 an account of observations he had made on the refractive index of 

 water at temperatures between 30 and 0. He used an interference 

 method, and found that as the water cooled the index increased. 



" La masse totale de 1'eau qui d'abord etait a 12 degres, se refroi- 

 dissant continuellement, arriva bientot a 4 degres, c'est-a-dire, au 

 point oii les variations de Tin dice devraient changer de signe, et ou le 

 deplacement des franges devrait etre inverse. Mais rien de pareil ne se 

 montra, et en continuant le refroidissement jusqu'a zero, on continua 

 d'observer une augmentation de 1'indice. II n'y a done pas de 

 maximum dans la valeur du coefficient de refraction quand il y en a 

 un dans la densite." 



In another experiment the temperature of the column of water 

 through which one of the beams of light passed was kept at r 

 whilst that of the other was gradually raised to 30 ; he found by the 

 displacement of the bands that the index decreased steadily. He did 

 not, apparently, publish any numerical values for the indices, bat 

 states that they are accurately given by the empirical formula 

 K, = K - (0-000012573)*- (0-000001929)* 3 . 



Two years later Gladstone and Dale (' Phil. Trans.,' 1858, p. 887) 

 gave an account of observations that they had made " on the 

 influence of temperature on the refraction of light;" they used a 

 hollow glass prism, and determined the angles of minimum deviation 

 for water, and several other liquids, at various temperatures. They 

 say, " our determinations were performed repeatedly and most care- 

 fully on water near the freezing point ; they confirm the observations 



