nilLOSOPHlCAL SOCIETY OF WASHINGTON. 321 



between stars in a probably diflferent state of condensation or of 

 specific gravity. 



A few years later, he continued his investigation of this sul)ject 

 of radiation, more especially with reference to Rumford's " Ob- 

 servations relative to the means of increasing the quantities of 

 Heat obtained in the Combustion of Fuel :" published in Great 

 Britain in 1802.* He found that Rumford's recommendation of 

 the introduction of balls of clay or of fire brick (about two and a 

 half inches in diameter) into a coal fire, was fully justified as an 

 economic measure : more heat being thereby radiated from the 

 fire into the room, and less being carried up the flue. He also 

 showed however that for culinary purposes, while the incandes- 

 cent or heated clay increases the radiation, and thereby improves 

 the quality of the fire for roasting, it correspondingly expends 

 the temperature, and thereby diminishes its power for boiling. 

 " That a solid substance increases the radiation of the heat of a 

 flame, is an interesting fact in connection with the nature of heat 

 itself. It would seem to show that the vibrations of gross matter 

 are necessary to give sufficient intensity of impulse to produce 

 the phenomena of ordinary radiant heat."r 



In 1851, he read before the American Association at Albany, 

 a paper " On the Theory of the so-called Imponderables :" (mainly 

 a development of his earlier discussion in 1846, of the molecular 

 constitution of matter,) in which he forcibly criticised a frequent 

 tendency to assume or multiply unknown and unrealizable modes 

 of action: holding that with regard to the most subtle agencies 

 of nature, we have no warrant by the strict scientific method, for 

 resorting to other than the observed and established laws of matter 

 and force, until it has been exhaustively demonstrated that these 

 are insufficient : and that time has not yet come. The funda- 

 mental laws of mechanical philosophy "are five in number; viz., 

 the two laws of force — attraction, nnd repulsion, varying with 

 some function of the distance ; and secondly, the three laws of 

 motion — the law of inertia, of the co-existence of motions, and of 

 action and re-action. Of these laws we can give no explanation : 

 they are at present considered as ultimate facts ; to which all 

 mechanical phenomena are referred, or from which they are de- 

 duced by logical inference. The existence of these laws as has 

 been said, is deduced from the phenomena of the operations of 

 matter in masses ; but we apply them by analogy to the minute 

 and invisible portions of matter which constitute the atoms or 

 molecules of gases, and we find that the inferences from this as- 

 sumption are borne out by the results of experience." He re- 

 garded the modern kinetic or dynamic theory of gases, by its 



* Jonrunl Roi/a! Instilution, 1802, vol. i. p. 28. 



t Proceed. Am. Assoc. Providence, Ant;. 1855, pp. 112-116. "On the 

 ElTect of luingling Radiating substances with Combustible materials." 



101 



