W. A. Norton on Molecular Physics. 219 
May it not be that the explanation of the possible existence 
of light without heat, thus made out, is to be found in the pres- 
Tay must also result from transverse vibrations; but this does 
Aot appear to be a legitimate conclusion if we adopt Professor 
Challis’s theor , that the Juminiferous ether is a highly elastic 
fluid, having the same properties as elastic fluids in general, an 
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 sta 
°y cannot neutralize each other, and must develop direct vibra- 
tions, which will take the place of those which counteract each 
other, and will exert a calorific action. In fact, Prof. Challis 
Conceives that “heat is the result of the mechanical action of 
the direct vibrations;” while “light is due to the transverse 
2? 
