Intelligence and Miscellaneous Articles, 54:7 



In the present note I communicate the results I have obtained for 

 collision with balls of diiferent metals. 



The method of experimenting was the same as that which I 

 described in my previous memoir. The weight of each of the balls 

 was the same ; and they fell from the same height upon the flat and 

 well-polished face, as hard as glass, of a solid cylinder of steel. The 

 balls not all having the same radius, it would be necessary to make a 

 correction in order to render the conditions equal, since the duration 

 of the impact depends on the curvature of the surface. From the 

 results which have been stated elsewhere, it follows that this cor- 

 rection would be very small (lead and zinc, 2| per cent.), and that in 

 all cases it may be neglected by the side of the other causes of error 

 presented by these metals when the limit of elasticity is exceeded. 



In fact, even with very small heights of fall, such as those which I 

 emjloyed (about 10 millims.), the softest metals undergo a slight 

 permanent deformation, which complicates the result. To render 

 the exjieriments comparable with each other, I always caused the 

 balls to strike with a fresh })ortion of their surface. 



I commenced by investigating the influence which might be 

 exerted upon the deflection of the magnetized needle by the thermo- 

 electric current produced by the contact of heterogeneous metals at 

 diff"erent temperatures. When the ball was put in prolonged con- 

 tact with the surface of collision connected, like it, with a galva- 

 nometer, a slight difference of temperature (such as that resulting 

 from the heating of the hand) sufficed to give the needle an oscillation 

 of 100°. But when the ball only remained on the surface of contact 

 during the shock, there was no perceptible current, even when it 

 rebounded as many as ten times in succession on the plane surface of 

 the steel. 



Nevertheless, in order to demonstrate clearly that no thermo- 

 electric current affected the experiments, the ball was heated to 

 about 200° before making it strike. Even in this case there was 

 nothing perceptible at the galvanometer, although the shocks sue- 

 ceeded each other rapidly. The experiments with the heated silver 

 ball were repeated after the insertion of a hydroelectric element in 

 the circuit : it is evident that the duration of the collision was then 

 augmented by the heating of the ball ; but the greater deflection of 

 the needle must not in this case be attributed to a thermoelectric 

 current, but, as we shall see, to a diminution of the elasticity in con- 

 sequence of the rise of temperature. For these experiments, balls 

 first cast and then turned were employed, of the following metals: — 



Coefficient of 

 Ball. elasticity, E. 



Steel 1960J 



Copper 10500 



Zinc 8700 



Brass 8540 



Silver 7140 



Tin 4000 



Lead 1700 



2 N 2 



