﻿368 G. K. Wead — Time of contact, etc. 



The observations for c'" are explained by the fact that the 

 gold foil stuck to the wires and so increased the time of contact 

 abnormally, but the time decreased as the foil was torn away. 

 In all cases there was a slight click (much most easily noticed 

 in the higher notes) showing that the addition of the foil, thin 

 as it was, changed the quality somewhat. 



The observations on C / were quite satisfactory and establish 

 the unexpected fact that the contact-time for a very soft stroke 

 is about 20 per cent greater than for an ordinary or hard blow 

 (the very few contradictory observations on higher notes are not 

 sufficient to disprove this conclusion) ; for an ordinary blow on 

 this string' the time is just } of the period instead of *21 as 

 Helmholtz estimated. 



Note ok Collision Experiments. 



While the apparatus used in the above experiments on the 

 piano was set up, a measure was made of the time of collision 

 between two ivory balls such as are used in the ordinary class- 

 room experiments. Several experimenters have published 

 their results for metallic balls, but I have seen none for ivory 

 balls ; and as such observations are fitted to do something to- 

 ward clearing up, in the student's mind, the rather hazy sub- 

 ject of impulsive forces and their measurement, I add my 

 results. 



The constants for determining the time were the same as 

 above except that K=15 ohms. 



#= 20 div. 

 .-. t— -00129 sec. 

 The diam. of the ball = <fc3'9 cm. 

 Its mass =m = 55 gms. 



The radius of the arc over which the balls swung =67'5 cm. 

 The chord of the arc =20 - 5 cm. 



.-. Final velocity = v = 18-2 cm. per sec. 

 m v= 4301 C. G. S. units. 

 Average force during contact = rnvs-t =3216000 dynes =3340 



gms. 

 Maximum force =6680 gms. approximately. 

 Compression of ball =s=ivt =*05 cm. approximately. 

 Diameter of circle of contact = 2^/ds='89 cm. approximately. 

 Malone, N. T., Sept., 1886. 



