528 



Mr. H. S. Allen on the Motion of 



A similar tube for increasing the height of fall was pro- 

 vided for the timing-sphere. 



. In" Plate I. fig. 1, one of these two tubes may be seen 

 supported by a retort-stand, on the extreme left of the picture. 

 . The dimensions of the glass vessel first used were as 

 follows : — length 11*5 centim., width (from front to back) 

 3 centim., depth 28 centim., all internal measurements. The 

 internal diameter of the tube used to produce a higher fall 

 was 2*4 centim. 



An increase in the height of fall from 34 centim. to 46 

 centim. produced an increase in the velocity of the largest 

 ball of less than 1 per cent. It was therefore assumed that 

 with a fall of 45 centim. (the vertical distance from the electro- 

 magnet to the top of the rectangular aperture) all the balls 

 would have practically attained their terminal velocity. The 

 results are given in Table VII., but it should be noted that 

 the velocities of balls Y. and VI. were obtained from falls of 

 23'9 and 21*2 centim., respectively. 



The dimensions of the balls are given later in Table VIII. 



Table VII. 

 ►Steel Balls in Water. — Small Vessel. 





Velocity V. 



logV. 



log a V. 



Temperature. 1 



- I. .'. 



II 



cm. /sec. 

 128-0 



121-6 



1165 



102-3 



954 



831 



2-1073 

 2-0849 

 2-0665 

 2-0100 

 1-9797 

 1-9191 



1-7051 

 1-5864 

 1-5114 

 1-3864 

 1-2793 

 1-1208 



11-2 0. 

 14-6 C. 

 14-6 0. 

 140 C. 

 18-9 C. 

 17-8 C. 



Ill 



IV 



V 



VI 





The object aimed at in the experiments was to approach, 

 as far as practicable, the ideal case of a sphere falling in a 

 fluid of infinite extent. The width of the glass vessel in the 

 experiments already quoted was only four times the diameter 

 of the largest sphere. It might, therefore, fairly be pre- 

 sumed that the walls of the vessel would have considerable 

 influence on the motion of the fluid, and consequently on the 

 velocity of the sphere. In order to test this point, a larger 

 vessel was constructed 11*5 centim. long, 6 centim. wide (from 

 back-to front), and 21 centim. deep. A wider fall-tube was. 



