430 Prof. Norton on Molecular Physics. 



greater intensity, are capable of penetrating to the atoms of 

 the medium and exercising a calorific action upon them. 



It is generally admitted that vision is produced by the trans- 

 verse vibrations of the rays of light. The fact that when two 

 rays of heat, polarized in perpendicular planes, meet in opposite 

 states of vibration they do not neutralize each other, has been 

 generally regarded as an indication that the calorific action of a 

 ray must also result from transverse vibrations ; but this does 

 not appear to be a legitimate conclusion, if we adopt Professor 

 ChalhVs theory, that the luminiferous aether is a highly elastic 

 fluid, having the same properties as elastic fluids in general, and 

 that the ^ethereal undulations consist of simultaneous longitudinal 

 and transverse vibrations, attended with variations in the density 

 of the medium, as in the case of waves of sound. For if trans- 

 verse vibrations, in perpendicular planes, meet in opposite states 

 they cannot neutralize each other, and must develope direct vibra- 

 tions, which will take the place of those which counteract each 

 other and will exert a calorific action. In fact Prof. Challis con- 

 ceives that "heat is the result of the mechanical action of the direct 

 vibrations;" while "light is due to the transverse vibrations." 



The intimate association of heat and light leads to the infer- 

 ence that they emanate from the same source, viz. the mole- 

 cular atmospheres of bodies; and if, as has been intimated, the 

 two emanations are essentially the same, we infer that rays of 

 light as well as of heat originate in vibratory movements of 

 the atomettes of these atmospheres. The atomettes lying at 

 different distances from the central atom of a molecule will have 

 different rates of vibration, increasing with the distance ; and so 

 the waves proceeding from them will have every variety of pul- 

 sation between the lowest limit, answering to the bottom, and 

 the highest, answering to the top of a molecular atmosphere. 

 Accordingly the red rays will proceed from the lower portions 

 of the atmosphere, and the violet from more elevated portions. 



If the electric atmospheres diminish in density by insensible 

 degrees from bottom to top, there should be no break in the con- 

 tinuity of the rays between the two extremes. But we know, 

 from the existence of bright bands in the spectra obtained from 

 coloured flames and from the highly heated vapours of metals 

 and other substances, that the rates of vibration of the luminous 

 rays given off by incandescent vapours seldom, if ever, vary by 

 insensible degrees from one extreme to the other. -We must 

 conclude therefore that the electric atmospheres of highly heated 

 molecules are made up of distinct layers of unequal density. 



Phenomena attending the propagation of light. — The absorp- 

 tion of light by a medium may be regarded as the taking up of 

 the sethereal pulses by the electric atmospheres of the medium. 



