102 WRITINGS OF JOSEPH HENRY. [1855- 



of the heat of temperature or expansion. When, as we 

 have previously indicated, the vibrations of the atoms of solids 

 become sufficiently violent to throw them beyond the sphere 

 of cohesion, the matter is converted from a solid into an 

 aeriform condition. 



But the question naturally arises, What is it that puts 

 in vibration the luminous body (a candle, for instance) and 

 keeps it for several hours in this constant state of agitation? 

 The answer is, the continued rushing together of atom after 

 atom of the carbon and hydrogen of the candle, and those 

 of the oxygen of the surrounding air. An action of a 

 somewhat similar kind, we must infer from analogy, is con- 

 stantly producing impulses of a like character at the surface 

 of the sun.. 



From the analogies of light, heat, and sound, we might 

 infer, since there are different lengths of waves of the latter 

 which give rise to the different notes of music, that there 

 are different lengths of waves of the setherial medium pro- 

 ducing different sensations in us, and different effects upon 

 gross matter. And this furnishes a ready explanation of 

 the well-known phenomena of the different colors of the 

 spectrum, and also of the less familar but equally remark- 

 able phenomena of the different kinds of radiant heat, as 

 well as of the chemical and phosphorogenic emanations 

 from the sun. 



That there may be different forms of waves transmitted 

 through the same medium will be evident from inspecting 

 the following figure, and considering the motions of the 

 atoms which may be produced by a single impulse. 



If we strike for example the atom a, it will be driven 

 towards the second atom, and the second towards the third, 

 the third towards the fourth, and so on; the motion will be 

 transmitted along the central line of atoms to the other ex- 



