PHYSICS. 337 



time of this extension and that of ai)plyinj>- tlie load becomes greater; 



(2) this increase of elasticity is ])roportioualIy greater for large loads; 



(3) it takes place eqnally whether the wh'e be loaded or unloaded in the 

 interval; (4) its rate of increase varies with different metals; (,">) the 

 elasticity can be increased by loading and unloading several times; (0) 

 a departure from Hooke's law always attends recent permanent exten- 

 sion and; (7) this departure is diminished, notably in iron, by allowing 

 the wire to rest for some time either loaded or unloaded. The intluence 

 of electricity and of magnetism on the torsional rigidity of metals was 

 examined, and the results showed (1) that in the case of copper and 

 iron the torsional rigiditj^ is temporarilj' decreased by the passage of a 

 strong current; (2) that of iron is temi)orarily diminished by a high 

 magnetizing force; and (3) these effects are independent of temperature 

 changes. {Mature, May 19, 1881, xxiv, 70.) 



Anderson has presented to a committee of the Institution of Mechan- 

 ical Engineers a report on the hardening and tempering of steel, in which, 

 after discussing the theories already proposed to account for the phe- 

 nomena, he proposes a new one, suggested by Edison's experiments on 

 platinum wire. It is a generally accepted fact that ordinary steel con- 

 tains a certain quantity of occluded gases, hydrogen, nitrogen, and car- 

 bonous oxide. The new theory supposes that by the application of 

 heat, these gases are expelled through minute Assures, wbich open in 

 the steel as the fissures opened in Edison's platinum wire. Sudden 

 cooling prevents their reabsorption, and perhaps assists, too, in the 

 expulsion. By the loss of these gases the metal becomes harder and 

 denser than before. If, now, the metal be exj)anded by gentle heating, 

 the fissures open and reabsorption begins ; the various changes which 

 the surface undergoes, as shown by the color-changes, being exponents 

 of the reabsorption i^rocess. Experiments are to be made by the com- 

 mittee to test the validity of this ingenious theory. [Nature, May 5, 

 1881, xxiv, 21.) 



Ewiug has devised a simple ibrm of speed-governor for continuous 

 motion. At the end of the vertical axis whose speed is to be controlled, 

 is a cross-bar carrying bell-cranks at its ends. The two vertical sides 

 of these carry balls united at top by a spring. The horizontal portions 

 carry paddles, dii>ping into an annular trough of glycerin. When the 

 speed is increased the balls separate, and the paddles being immersed 

 deeper in the glycerin; the velocity is diminished. {Nature, March 17, 

 1881, xxiii, 473.) 



Holtz has determined the modulus of elasticity of the carbon rods 

 made by Carr6 and used for the electric light. The acoustic method 

 was used, the rods being held in the middle and vibrated longitudinally 

 by rubbing with a resined cloth. On the average the modulus was 

 found to be about the same as that of lead; though in the thinner rods 

 the density is greater, and so the modulus is higher. Heat developed 



by the fricti®n raises the tone. ( Wiedcmami's Annalcn, 1881, i, .) 



S. Mis. 109 22 



