336 RECORD OF SCIENCE FOR 1886. 



per square millimeter. (Wied. Ann., 1885, xxv, 438; J. Pbys., Novem- 

 ber, 1886, II, V, 484.) 



Scbneebels Uas experimentally verified the conclusions of Herz con- 

 ceruiug the impact of elastic bodies. The duration of the contact of 

 two spheres 70™'" in diameter was determined by the impulse given to 

 a galvanometer ueedle by a current which passed between the spheres 

 while they were in contact. Provided the total resistance of the cir- 

 cuit is large and the coefficient of self-induction small, the time may be 

 considered proportional to the deviation of the needle. With velocities 

 varying from 156"^"' to 1,032"'™ the deviations observed varied from 59.0 

 to 39.5, the product of the deviation and the fifth root of the velocity be- 

 ing sensibly constant. With spheres of different diameters and the same 

 velocity the ratio of the diameter to the deviation was fonnd to be con- 

 stant. In order to determine the absolnte duration of the contact, the 

 author compared the impulse produced by the impact with that given 

 by a pendulum sliding on a steel band during 0.00082 second, and thus 

 obtained 0.000185 second. He has verified also the formula of Herz, 

 which gives the radius of the surface of flattening in terms of the radius 

 of the sphere. The spheres were covered with i)araffin and the .radius 

 of the circle iiroduced by the impact was measured micrometrically. 

 For a velocity of 259™™ the radius observed was 0.6G™™; that calcu- 

 lated being 0.65. For a velocity of 518""" the radii were 0.83 and 0.85, 

 respectively. For 1,042™'", 1.10 and 1.12"'™, and for 1,535""" velocity, 

 1.31 and 1.27"'"'. In the case of the higher velocities, these results are 

 interesting, since the pressure obtained surpasses that ordinarily as- 

 sumed as the limit of the elasticity of the steel. (Arch. Sci. Phys. Nat., 

 Geneve, 1885, xiv, 435; J. Phys., June, 1886, II, v, 201.) 



Tomlinson has communicated to the London Physical Society the 

 results of a long series of experiments on the torsional elasticity and 

 the internal friction of metals, in the course of which he had noticed 

 several sources of error incident to torsional experiments. In the earlier 

 experiments a horizontal brass bar was suspended by a wire and oscil- 

 lated, the time of vibration being observed by means of a lamp, scale, 

 and mirror. Its moment of inertia was varied by sliding two brass 

 cylinders, susi)ended from the bar by tine wires, backward or forward 

 along it. Under certain conditions it was observed that the bar exe- 

 cuted a few vibrations of gradually decreasing amplitude, came to rest 

 and then commenced to swing again, the amplitude increasing to a 

 maximum, then decreasing, and so on. This effect was finally traced 

 to an approach to synchronism between the time of oscillation of the 

 bar and that of the small cylinders about tlieir axes of suspension, the 

 absorption of energy being due to these being set in vibration. On 

 clamping the cylinders rigidly to the bar the phenomenon disappeared." 

 Subsequently something of the same kind appeared which turned out 

 on investigation to be due to an approach to synchronism between 

 the torsional and the pendulous vibration periods. Of course this could 



