a scientific subject. The Council, in discharge of the powers 

 vested in them, have awarded unanimously the Keith prize for 

 the last biennial period, to Professor Forbes, for his paper " On 

 the Refraction and Polarization of Heat,'' which they consider 

 to come under that class of communications, which contain dis- 

 coveries important to science. 



The Vice-president then observed, that the subject of heat is 

 one so important to man, and so intimately connected with a va- 

 riety of natural phenomena, that it has not failed to command 

 no small degree of attention in all ages. That an intimate con- 

 nexion subsists between Heat and Light, and that much discord- 

 ance of opinion has subsisted respecting the nature of both. He 

 next stated the various opinions entertained concerning them, 

 and particularly respecting heat, and in historic order presented 

 the views of Bacon, Boyle, Boerhaave, Stahl, and Black, and ad- 

 verted to the discoveries of Black respecting latent and specific 

 heat, and the successive labours of Irvine, Crawfurd, Wilke, 

 Magellan, Lavoisier and Laplace, Dulong and Petit, in the 



same field. 



Heat presents itself in two very different conditions ; first when 

 combined with matter, pervading bodies slowly, either by com- 

 munication and conduction through and among its particles, or 

 by the movements of the particles themselves ; secondly, when 

 radiated, moving through elastic fluids or empty space with vast 



velocity. 



The first of these had been studied by the philosophers al- 

 ready named, and not long after by Rumford. To the second 

 of these, viz. radiant heat, the subject of Professor Forbes's dis- 

 covery called upon him more especially to allude, and to pre- 

 sent a brief historic view. 



The radiation of cold, and its reflection by metallic mirrors, 

 was known to Baptista Porta in the sixteenth century ; and ob- 

 servations were made on the radiation of heat, by the Florentine 

 academicians, towards the middle of the seventeenth century, 

 and by Marriotte in 1 682. About the middle of the 18th cen- 

 tury, Lambert published his works on pyrometry and photome- 

 try, which contained some of the first accurate experiments on 

 this subject ; and the facts of the difficult transmission and re- 



