Barrett — Amozmt of Light Scattered from Rough Surfaces. 191 



by different surfaces. The estimates given were variable, and appeared untrust- 

 worthy ; nor could I fiud by what method of observation they were arrived 

 at. One difBculty has arisen from tlie fact that the ordinary photometric 

 method, which involves the law of inverse squares, is inapplicable to large 



Fio. 1. 



reflecting surfaces. A modification of that method is possible by receiving 

 the scattered light upon a small screen of ground glass or tracing-paper, and 

 using this as the source of light which can be balanced against a standard 



2i2 



