ART' 8.— S. NAKAMURA. 



the assumption that k is independent of u. But as my present circu- 

 mstances do not allow me to repeat the experiments and confirm the 

 results hitherto obtained, I shall not at present, insist on the last 

 statement. Let me describe my arrangement and the method of 

 deducing h. 



In the accompanying figure 1, P is a prism glass ; Q and R are 

 made of any solid and of such size that when they are packed and 

 pressed together slightly, the hollow space in Q, forms a closed rec- 

 tangular water tight diffusion vessel bounded on one side by the prism 

 Fig. 1. P and on the other by the plate 



R. H is a hole for introducing 

 the liquid, and is to be closed 

 by a stopper. K is a hole bored 

 in R, for admitting a thermo- 

 meter. It does not communi- 

 cate with the hollow space in 

 Q, in order to keep the area of 



the cross section of the diffusion vessel constant. 



When a pencil of light is sent horizontally through the Rice b 



(tig 2) of the prism, it is reflected at the face c, where the glass is in 



contact with the liquid, and then emerges from the prism through the 



Fig. 2. face a. When the prism is optically denser than 



the liquid, total reflection will take place. Let 



EF be the emergent ray corresponding to the 



critical ray. If N and // be the indices of reflection 



-K of the glass and of the liquid respectively, and if 



the angle ABC of the prism be a and the angle 



FEG be d, then 



