82 



19th January. 

 Dr hope, V.R, in Chair. 



The following Donations were presented : — 

 Report to the Committee of the Commissioners of Northern Lights, 



appointed to take into consideration the subject of Illuminating 



the Lighthouses by means of Lenses. By Alan Stevenson, M.A., 



Civil-Eno'ineer. 

 Bulletin de la Societe G-eologique de France. Tome iv. Feuilles 



28, 29. 



The following Communications were read : — 

 1. On the Refraction and Polarization of Heat. By 

 Professor Forbes. 



The First Section of this paper contains an account of a variety 

 of experinn nts undertaken with the thermo-multiplier of Nobili and 

 Melloni, the instrument exclusively employed in the subsequent re- 

 searches. By a comparison of its sensibility with that of air-thermo- 

 meters, the author concludes that one degree of deviation of the 

 needle of the multiplier corresponds to an effect indicated by about 

 one-fiftieth of a centigrade degree on the others. Without increas- 

 ing the dimensions of the multiplier, by which its sensibility would 

 be impaired, he has been enabled, by an optical contrivance, readily 

 to measure one-tenth of one of its degrees, corresponding to one-five- 

 hundredth of a centigrade degree. From an experiment intended 

 to detect the htat of the lunar rays, concentrated by a polyzonal lens, 

 thirty-two inches in diameter, and acting upon this instrument, he 

 concludes that the direct effect of the moon upon an air-thermometer 

 probably does not amount to one-three hundred thousandth part of 

 a centigrade deoree. 



After mentioning his repetition of M. Milloni's experiments ujion 

 the refraction of heat, the author proceeds, in the Second Section, 

 to give an account of his own researches on the action of tourmaline 

 on heat. At first he found (as it afterwards appeared M. Melloni 

 had done) that no more heat was stopped when the tourmaline plates 

 had their axes crossed, or transmitted least light, than when they 

 were parallel, or transmitted most. He afterwards detected a fallacy 

 in his mode of operation, and proved the polai'ization of heat, whe- 

 ther luminous or obscure, by tourmaline. 



The Third Section treats of the polarization of heat by relraction 



