142 Royal Institution : — 



are produced, and that the amount of heat very rapidly increases 

 with the intensity of these condensations and rarefactions. 



It has further been established that various bodies exhibit a 

 greater increase in temperature after being sounded the more ra- 

 pidly their sound fades away, or, what a is the same, the more they 

 deaden the sound of other bodies ; the greatness of the differ- 

 ence in the increase of temperature observed justifies the state- 

 ment that the larger increments of temperature do not depend 

 upon a smaller specific heat of the bodies in question, but on the 

 fact that a greater quantity of heat is produced when they are 

 sounded. 



In comparing the various bodies as regards the quantity of 

 heat produced by sounding, it is remarked that the production 

 of heat in bodies is greater the smaller the velocity of sound in 

 them ; it is greatest in caoutchouc, in which sound scarcely tra- 

 vels 40 metres in a second. This is connected with the fact that 

 the wave-length diminishes with the velocity of sound, and that, 

 if bodies are sounded with the same force, the condensations and 

 rarefactions must be greater in the shorter than in the longer 

 waves. 



It is also possible that specific differences in substance may 

 contribute their share to the difference in the production of heat 

 in various bodies. 



XVII. Proceedings of Learned Societies. 



ROYAL INSTITUTION OF GREAT BRITAIN. 



May 28, /~^N Recent Discoveries in Solar Physics made by means 

 1869. ^-^ of the Spectroscope. By J. Norman Lockyer, F.R.S. 



In the year 1865 two very important memoirs dealing with all the 

 telescopic and photographic observations accumulated up to that 

 time on the subject of solar physics were given to the world. One 

 of them was privately printed in this country ; the other appeared in 

 the Comptes Rendus of the Paris Academy of Sciences. 



I shall not detain you with a lengthened notice of these remark- 

 able papers. I shall merely refer to the explanation given in both 

 of them of the reason that a sun-spot appears dark — the very key- 

 stone of any hypothesis dealing with the physical constitution of 

 the sun. 



English science, represented by Messrs. De La Rue, Stewart, and 

 Loewy, said that a spot is dark because the solar light is absorbed 

 by a cool, non-luminous, absorbing atmosphere, pouring down there 

 on to the visible surface of the sun, in other words, on to the photo- 

 sphere. 



French science, represented by M. Faye, said that a spot is dark 

 because it is a hole in the photosphere, and the feebly luminous and, 

 therefore, radiating interior gases of the sun are there alone visible. 



