308 THOMAS YOUNG. 
observe only a partial weakening of intensity, sometimes, 
on the other hand, the rays conspire and increase the 
illumination. Every thing depends on the difference in 
the length of route which they have gone through, and 
0 
' 
. 
each other in the inside of the shadow; in either case giving stripes — 
or bands. To complete the proof, when an opaque screen was placed 
so as to intercept the rays on one side, though abundance of light was 
present on the other, yet all the internal bands immediately disap- 
peared; demonstrating that the effect was due solely to the concur- 
rence of the light from both sides. The bands produced by light 
admitted through narrow apertures, and numerous other phenomena 
of the same kind, may receive a general and popular explanation in 
the same way.— Translator. 
* 
