110 On the Powers of Steam, &c. 



XIX. On the Powers of Steam, in communicating heat . 

 to bodies, with which it comes in contact. By Ro- 

 bert M'Causland, M. D., and by him commu- 

 nicated to the Editor, in 1787. 



IT is, I believe, to Dr. Black that the world 

 is indebted for new ideas, and new language, in res- 

 pect to some of the phenomena of heat. The clue 

 which he has furnished is, perhaps, more extensive 

 in its effects than some have supposed ; and there 

 are many appearances in nature, which, although 

 they have long been perfectly familiar to us, do, ne- 

 vertheless, seem to be inexplicable upon any other 

 principles than those which have, some time ago, 

 been laid down by him. He has shown, 



1st. That at the very instant in which bodies pass 

 from the state of vapour to the state of liquid, a large 

 quantity of heat emerges from them, and passes im- 

 mediately into any bodies that happen to be conti- 

 guous. 



2dly. That this same liquid, in passing into a state 

 of solidity, again parts with a quantity of heat. 



3dly. That before a solid can acquire a liquid state, 

 it must absorb a large quantity of heat ; which sup- 

 ply of heat, being drawn from surrounding bodies, 

 will have considerable effects in lowering their tem- 

 perature. 



