TRANSACTIONS OF THE SECTIONS. 



535 



ing to their chords, each way, starting from the lowest point, 

 the point of junction of the balls when still; since the velo- 

 cities acquired by bodies falling doM^n those arcs are as their 



chords. In the experiments with the larger balls, two persons 

 usually supported the balls at any points, G, H, of equal height, 

 as directed, and let them fall at the instant that a sharp blow 

 was given on the wall for a signal, the author and another 

 person observing the points E, F, to which the balls returned 

 after having impinged at the lowest point. The chords of the 

 arc, fallen through and returned, were, as mentioned above, 

 considered as the measures of the velocities of impact and re- 

 coil. In some of the experiments one of the balls was at rest 

 at the lowest point, before impact. The resistance of the air, 

 in the lighter bodies especially, was generally allowed for. 



In the tabulated results of experiments accompanying this, 

 each number set down for the elasticity is the greatest from 

 about ten impacts ; and in the smaller balls, especially in the 

 greater arcs, it is often from as many as twenty, on account of 

 the difficulty of obtaining, with large arcs, direct and central 

 impacts. 



Conclusions from the Experiments referring to the "Tabulated 

 Results" for proofs and illustrations. 



Conclusion 1 . All rigid bodies are possessed of some de- 

 gree of elasticity ; and among bodies of the same nature, the 

 hardest are generally the most elastic. 



This conclusion obtains a good illustration from metals. 

 Thus, the soft metal lead has an elasticity of -20, as exhibited 

 by its mean ratio ; brass, which is harder than lead, has its 

 elasticity '36 ; bell-metal, which is harder than brass, has '59 ; 

 cast iron, still harder, has -66 ; and steel, the hardest metal of 

 all, has -79 for its elasticity. (Expts. 13, 10, 12, 1 to 3, 31.) 

 The same conclusions might be drawn from the elasticities of 



