502 — THOMAS YOUNG. 
The theory of Thomas Young is not amenable to this 
criticism. Here there is no longer admitted any peculiar 
kind of “fits” as primordial properties of the rays. 
The thin film is here assimilated in all respects to any 
thicker reflector of the same substance. If at certain 
points in its surface no light is visible, Young did not 
conclude that therefore its reflexion had ceased ; he sup- 
posed that, in the special directions of those points, the 
rays reflected by the second surface proceeded to meet 
with those reflected from the first surface, and com- 
pletely destroyed them. This conflict of the rays is 
what the author designated by the term “ interference,” 
which has since become so famous. » 
Observe then here the most singular of hypotheses! 
We must certainly feel surprised at finding night in full 
sunshine, at points where the rays of that luminary 
arrive freely ; but who would have imagined that we 
should thence come to suppose that darkness could be 
engendered by adding light to light! 
A physicist is truly eminent when he is able to an- 
nounce any result which, to such an extent, clashes with 
all received ideas; but he ought, without delay, to sup- 
port his views by demonstrative proofs, under the pen- 
alty of being assimilated to those Oriental writers whose 
fantastic reveries charmed the thousand and one nights 
of the Sultan Schahriar. 
It was nothing more than the strict inference that at those points suc- 
cessively something occurred in the course of the ray which disposed it 
for, or induced, reflexion in the one case, and non-reflexion in the 
other; accompanied in the latter case by the like tendency to trans- 
mission. These apparent “ fits’? must be still acknowledged as phe- 
nomena; the mechanism by which they are produced is, however, now 
known to be nothing inherent in the light, no essential property re- 
curring, but the simple periodicity of conspiring or counteracting 
wave-action.— Translator. 
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