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IOWA ACADEMY OF SCIENCE 



ter a nitrogen filled tungsten lamp was employed placed 

 in a light-tight b< x is i - :I by a lens. L. at the point- V 

 and H. This division of the ligh" - oomplished by means 

 mirror M. partly in1 tnng the light. .V. is a Nic - 



set - _ Passing thr 



ts the lens. L z and by it would be brought 

 - " t not i stal ] I at X. This latter 



- t ' .: ugh the totally reflecting prism. P and it 





-K - 



Fig 15. 



: the slit of the monoehro- 



. SE T ion of the original beam of light 



_ - enee through the lens /. . 



5 A", and V . the latter with an attached circular scale 



and lastly is focused by means of the lens L i upon 



- monochromator. These two 



5 pass 1 - lment and form on the emergent 



»es of 1 at slit., one above the other, and formed 



oming along the two separal The wave I - 



hich 02 ?hes 1 samination is obtain- 



» the g ted ?. The instrument had of course 



- two images are viewed through the 



5 to & for a wave length at 



then to rotate the Nicol, N . 



. - are matched in brightness. By proper 



