351 
ON THE ABSORPTION AND RADIATION OF 
HEAT. 
BY H. DEBUS, Fh.D., F.R.S. 
O UR knowledge of heat has received during the last few 
years considerable additions through the researches of 
Professor Tyndall, of the Royal Institution. The results of 
his investigations not only explain some of the grand opera- 
tions of nature, but also allow the philosopher a more correct 
estimation of molecular actions. The following contains a 
short account of Mr. Tyndall’s researches and results, and of 
the theoretical views by means of which the latter may be 
explained. Till very lately the majority of philosophers 
supposed heat to be an invisible substance, without weight, 
endowed with great elastic force, and corresponding tendency 
to expand. It was thought to surround the atoms of bodies 
like an atmosphere, and to fill the spaces between their 
molecules. On account of the simple explanations which this 
theory afforded of most of the phenomena of heat, it was able 
to maintain its position in the domain of science, even after 
the discovery of facts for which it was not able to account. 
Such facts are the production of heat by friction and per- 
cussion, and the conversion of heat into mechanical force. 
Count Rumford was struck by the great amount of heat 
developed by the boring of cannon, in one case sufficient 
to boil 18 f lb. of water, and Davy transformed ice into water 
by rubbing two pieces of ice together. In each case a very 
great quantity of heat was developed, and the question may 
be asked, ( \ [ whence did the heat come ?” 
Locke says, Heat is a very brisk agitation of the insensible 
parts of the object, which produce in us that sensation from 
whence we denominate the object hot : so what in our 
sensation is heat, in the object is nothing but motion A 
Bacon and Davy held similar views. The theory of heat now 
adopted by the most distinguished scientific authorities, 
considers heat to be a mode of motion of the infinitely small 
particles, called atoms or molecules, of which bodies are com- 
posed, the conduction of heat being the propagation of this 
motion from one part of the body to another. If we feel the 
