AET 8.— S. NAKAMUEA. 



For the subjective experiment and for the determination of 



fe, a different arrangement is necessary. The diffusion ves- 



Fig. 3. sel is to be furnished with 



adjustable tripods and placed 

 on a spectrometer. A sodium 

 flame is put before the face 6, 

 and directly in front of the 

 face a, a cathetometer is placed. 

 The telescope of the latter 

 is provided with an auto- 

 collimating ocular, which 

 is used for fixing the direction of the normal EG. When the 

 vessel is filled with a homogeneous liquid, on looking through 

 the telescope, one can at once see a sharply defined vertical 

 boundary between the total and the partial reflections. But when 

 the vessel is filled with the diffusing liquid, it is otherwise. With the 

 full aperture of the telescope, one can not distinctly see the bounday 

 which is curved in this case, for the evident reason that it is 

 crossed by the vertical rays. It is necessary to cut down the rays 

 entering the telescope to a narrow pencil in a horizontal plane. I 

 covered the objective with a cap having a horizontal slit about 1 mm. 

 broad, and only then was I able to see the diffusion curve distinctly. 

 With the telescope thus furnished with a slit, it is a very simple matter 

 to move the telescope vertically and measure the angles 6 at different 

 heights. 



In passing, it will be noticed that this method may also be used 

 for the study of diffusion through an opaque body like sand, or through 

 a substance like agar-agar, as investigated by Yoigtländer (1) . 



(1) Voigtläniler, Zeits. für phys. Chemie, 3. 1889. 



