646 ADDRESS OF PROFESSOR LOVERING. 
but it is said that comparison is not always a reason. It is not 
denied that, when the sonorous body is approaching, the sound 
waves are shortened, the number of impulses on the ear by the 
condensed air is increased, and the pitch of the sound is raised. 
Possibly, the color of light would follow the same law; but there 
is no experiment to prove it, and very little analogy exists between 
the eye and the ear. There is no analogy, whatever, between the 
subjective sensation by either organ and the physical action of the 
prism. The questions at issue are these :—Does refraction depend 
upon the absolute or the relative velocity of light; are the time 
of oscillation of the particles of ether and the normal wave-length, 
corresponding to it, changed by any motion of translation in the 
origin ; or is the conservation of these elements an essential attri- 
bute of the luminiferous medium. It has been said that Doppler 
reasoned as if the corpuscular theory of light were true, and then 
` expressed himself in the language of undulations. Evidently, 
there is an obscurity in the minds of many physicists, and an un- 
certainty in all, when they reason upon the mechanical constitution 
of the ether, and the fundamental laws of light. The mathemati- 
cal theory is not so clear as to be able to dispense with the illumi- 
nation of experiment. Within the present year, Van der Willigen 
has published a long and well considered memoir on the theore 
ical fallacies which vitiate the whole of Huggins’ argument for 
the motion of the stars and nebulae. His analysis proves that the 
motion of the luminary will not interfere with the time of oscilla- 
tion and the wave-length, provided that the origin of the disturb- 
ance is not a mathematical point but a vibrating molecule, and 
that the sphere of action of this molecule upon surrounding mole- 
cules is large enough to keep them under its influence during ten 
or a hundred vibrations, before it is withdrawn by the motion of 
translation. If this theoretical exposition of the subject should 
be generally adopted by mathematicians, the spectroscopic obser 
vations on the supposed motion of the stars must receive another 
interpretation. On the other hand „if a luminary is selected which : 
is known to move, independently of spectroscopic observations: 
and the displacement of the spectrum lines accords with this mo- 
tion, it will be time to reconsider the mathematical theory , and 
make our conceptions of the ether conform to the experiment : 
The Spectroscopic observation of Angstrom on an oblique a 
spark does not favor Huggins’ views. Secchi testifies to opPo* 
