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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 



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. 



