104 



Lastly, the same law is traced in the constitution of the chlorides 

 of the magnesian class of metals, which are found to have two equi- 

 valents of water strongly attached to them, and which may therefore 

 be considered as constitutional. Many of them have two or four 

 equivalents more, the proportion advancing by multiples of two 

 equivalents. 



Professor Graham has supported these views, not only by nume- 

 rous arguments, but also by experimental investigations of the phy- 

 sical properties of different classes of salts, and a great number of 

 chemical analyses ; and he has thus largely added to our positive 

 knowledge of this somewhat neglected branch of chemical science. 



The Council, without pronouncing any judgement on the ques- 

 tion whether Professor Graham's hypothesis concerning the differ- 

 ent functions of water in the constitution of salts be a representa- 

 tion of the real mechanism of nature, are of opinion, that the dis- 

 cussion of his new and ingenious views will be highly conducive to 

 the progress of science, particularly in the department of organic 

 chemistry, in which they have been already followed out with suc- 

 cess by some eminent foreign chemists, and have accordingly awarded 

 to Professor Graham the Royal Medal for Chemistry of the present 

 year, for his valuable researches in this department of science. 



The Council have awarded the Rumford Medal to Professor 

 Forbes, for his discoveries and investigations of the Polarization 

 and Double Refraction of Heat, published in the recent volumes of 

 the Transactions of the Royal Society of Edinburgh. 



That solar heat, like the light which it accompanies, may be po- 

 larized, was shown by the early experiments of MM. Malus and 

 Berard; but the announcement of M. Berard, that heat from other 

 sources was also capable of polarization, not having been confirmed 

 in subsequent repetitions of his experiments by other philosophers, 

 it became of the highest importance to establish this analogy be- 

 tween light and heat from whatever source the latter might be 

 derived. 



The admirable instrument, the Thermo-multiplier, invented by 

 MM. Nobili and Melloni, afforded facilities for the prosecution of 

 inquiries of this nature, of which the inventors and others were not 

 tardy in availing themselves. One of the most important results 

 obtained by M. Melloni, and confirmed by Professor Forbes, the 

 refrangibility of non-luminous heat by a prism of rock-salt, appeared 

 to point to the polarization and double refraction of heat as almost 

 necessary consequences. The experiments, however, of both these 

 philosophers with tourmaline, undertaken nearly at the same time, 

 appeared to negative the fact ; but Professor Forbes becoming sen- 

 sible of the source of error, in the conclusions he had at first drawn 

 from his experiments, soon saw that his results clearly indicated the 

 effect he was in search of. His subsequent experiments established 

 the fact, that in the transmission of heat from an Argand lamp, from 

 incandescent platinum, and even from non-luminous heated brass, 

 through slices of tourmaline cut parallel to the axis of the crystal, 



