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UNIVERSITY OF COLORADO STUDIES 



wedge-shaped compartments. The ends a h and c d are not quite 

 parallel to each other, so that if the two compartments are filled with 

 liquids having the same index of refraction there will be a slight 

 resultant refraction of the light rays that pass through the tube. The 

 rays of light that pass outside of the tube, therefore, will form an im- 

 age Sg a little to oue side of S^. It is evident that if the liquid in 

 one compartment (the wedge a c d for instance) is undergoing a 

 chemical change its index of refraction in general will vary and the 



Pig. 2. 



image S^ will move sideways. The distance that S^ has moved will 

 be a measure of the change that has taken place in the index of 

 refraction and, therefore, of the amount of substance in a c d, that 

 has reacted. The displacements of S^ can be determined by com- 

 paring its distances from Sg which remains stationary. 



In order to obtain a complete record of the position of S^ a pho- 

 tographic plate S^Sg is placed in a vertical position at the images S^ 

 and Sg and just in front of it a screen. A narrow horizontal slit cut 

 in the screen allows a small part of the light only to pass through. 

 At any instant of time, therefore, there will be two small spots of 

 light on the plate at the intersections of the two images S^ and S^ 

 with the projection of the slit on the plate. A system of cog-wheels 



