124 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



FIG. 2 



Sutherland has pointed out, a 

 fairer test of the correctness of 

 (III) might be made with a 

 viscosity apparatus like that 

 for which the formula was de- 

 duced. 



This suggestion has been fol- 

 lowed in the construction of the 

 instrument whose description 

 follows. 



Viscosity Apparatus — De- 

 scription. — The viscosity appa- 

 ratus used in these experiments 

 consists of two circular glass 

 plates 8.2 cm. in diameter and 

 0.3 cm. thick (A, Figure 2). 

 They are pierced by a hole in 

 the centre 0.3 cm. in diameter, 

 and by three holes near the 

 edge, equally spaced, and 0.15 

 cm. in diameter. Through the 

 latter are passed small threaded 

 platinum bolts, provided with 

 nuts, for the purpose of binding 

 the plates together. In order 

 that the latter may be fixed at 

 a certain distance apart, they 

 are separated by three short 

 glass tubes, through the bore 

 of each of which passes one 

 of the aforesaid bolts. These 

 glass tubes are ground to the 

 same length, 0.35 cm. 



These are the two fixed plates 

 in Maxwell's apparatus, while 

 between them, concentric with 

 them, and parallel to them, is 

 suspended the vibrating disk, 

 which consists of a plate of glass 

 4.4 cm. in diameter and 0.09 

 cm. thick. It has a hole in 



