236 FRESNEL. 
We may, indeed, fairly deduce from the absence of all 
rotation in the lever suspended by the spider’s thread, 
under the action of an enormous quantity of light, that 
the elementary particles of the luminous rays have not 
dimensions comparable to the millionth part of the finest 
molecules possessing any weight. But as there is nothing 
to show any absurdity in supposing them a million, or a 
myriad, times less than this, this kind of experiment and 
argument (the first idea of which is due to Franklin) 
cannot furnish any decisive conclusion. 
Among the objections which Euler has presented in 
‘his works against the theory of emission, I will point out 
two, on which he has particularly insisted, and which 
seem to him irresistible. “If the sun,” (said this great 
geometer,) “continually darts out particles of his own 
substance in every direction, and with enormous velocity, 
he must end by exhausting himself: and during the many 
ages which elapsed since the historical period, some dirai- 
nution ought already to have become sensible.” 
But is it not evident that this diminution depends on 
the magnitude of the particulars? Now there is nothing 
to hinder our supposing them of such small diameters 
that, after millions of years’ continual emission, the mass 
of the sun should not be sensibly altered. And, besides, 
there is no accurate observation to prove that this lumi- 
nary does not waste, or that its diameter is really as great 
as it was even in the time of Hipparchus. 
No one is ignorant of the fact, that millions of rays can 
penetrate together into a dark room through a pin-hole, 
and there form distinct images of external objects. In 
crossing each other in that minute space, the material 
elements of which we suppose this multitude of rays to 
consist ought, nevertheless, to encounter and clash against 
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