730 Dr. Gr. A. Shakespear: Experiments on the 



The catcher took the form of a calico sheet, about 70 cm. 

 square, attached to two laths, one at each o£ two opposite 

 sides of the square. One of these laths was fixed in a 

 horizontal position to a frame. The other was attached, by 

 a small chain at its centre, to the upper end of a vertical 

 steel strip, the lower end of which was fixed. This strip 

 had a platinum contact at its back which pressed against the 

 end of a screw, tipped with platinum, on a brass upright 

 attached to the frame. When the ball struck the tightly 

 stretched sheet the spring was pulled away from the screw, 

 and the primary circuit in which the two were included was 

 thus broken. 



In timing the simultaneity of fall of two spheres the eye 

 was a sufficiently accurate judge, except when the velocities 

 were greater than 1500 cm. /sec. In this case an automatic 

 indicator was used, made of two sheets similar to that above 

 described, placed end to end, the two outer edges being fixed 

 while the inner edges were attached to a stiff steel spring in 

 the form of a vertical strip. On the upper edge of this 

 strip, which was about '25 mm. thick, a knife-edge was 

 pressed by another spring, so that a slight movement of the 

 upright spring to one side or the other resulted in the falling 

 of the knife-edge on the opposite side of the spring. In 

 this way it was easy to see which sheet had been struck 

 first. The loading of the balls was so adjusted that in 

 successive falls the knife-edge fell sometimes on one side and 

 sometimes on the other. It was found that with velocities 

 of the order of 3000 cm. /sec. the judgment of the eye was 

 often wrong as tested by this double catcher. When the 

 two balls were used the horizontal distance between the lines 

 of fall was about 90 cm. One ball was taken as a standard 

 and each of the others in turn allowed to fall simultaneously 

 with this, the weights being adjusted till the two reached 

 the catcher together. The balls were then weighed. The 

 standard ball was then given a different weight and 

 the process repeated. 



Results. 



The results may be stated under three headings : — 

 (1) The relation between air resistance and velocity for 

 a sphere of 3*70 cm. diameter for velocities up to 

 1300 cm./sec. ; (2) the relation between air resistance and 

 diameter for spheres between 2 cm. and 7 cm. diameter at a 

 velocity of 1030 cm./sec. ; and (3) the relation between the 

 diameters and weights of different spheres which fall through 

 air in equal distances in equal times, the limiting velocities 

 not having been reached. 



