PHYSICS. ' 347 



the positive pole the rise was only 3'^. This rise of temperature iu the 

 light from the cathode, he thought, might be utilized to determiue the 

 degree of exhaustion. (Xatare, March, 18SG, xxxiii, 480.) 



ACOUSTICS. 



Bakmetieff has investigated the sounds which are produced by rods 

 of magnetic metal under the iutinence of intermittent magnetization. 

 He finds that the intensity of the sound diminishes by longitudinal 

 compression, iu the case of iron and of nickel rods. As to tension, it 

 diminishes indefinitely the intensity of the sound in nickel, but in iron 

 it causes it to diminish to a minimum only, and then as the tension in- 

 creases the sound becomes louder again. But, on the other hand, Joule 

 has shown that iron submitted to a certain tension no longer elongates 

 by magnetization; and farther that if the tension be still more increased 

 it actually shortens during magnetization. Barrett has shown, too, a 

 diminution of the length of a nickel rod by magnetization. Hence the 

 author concludes that it is the change of the length which is the cause 

 of the sound produced by intermittent magnetization. (J. Soc. Phys. 

 Chim. Eusse, 1885, xvii. Go; J. Phys., February, 1886, II, v, 91.) 



Semmola has observed that if a metallic plate or a sonorous cord be 

 traversed by very frequent discharges from an electric machine, they 

 give a sound which though very feeble is yet entirely distinct from the 

 noise of the spark. To hear this sound it is necessary to fix the metal 

 plate at the end of a sonorous collector of ebonite, which is brought 

 near the ear. The sounds become more acute in proportion as the dis- 

 charges succeed each other more frequently. Sound is also obtained 

 from a metal plate which is placed near to a conductor which is itself 

 traversed by electric discharges. The plate in this case should be con- 

 nected to earth, so that it may be said that the sounds which are thus 

 produced by induction are like the phenomena of the return shock. (C. 

 E., M;iy, 1880, Cii, 1059.) 



VioUe and Vautier have studied the propagation of sound in a cyl- 

 indrical tube 0.70 meter iu diameter designed to convey the water of 

 Eochefort to Grenoble. The portion of the conduit utilized consisted 

 of two straight parallel tubes, each 6.375 kilometers in length, which 

 could be used separately or joined at one end by a semicircular tube of 

 the same diameter. The receiving apparatus used was in part that of 

 Eegnault, with thinner membranes, and in part the mauometric tam- 

 bours of Marey. The sonorous wave was produced by means of mu- 

 sical instruments or pistol-shots. When a pistol is fired at one end a 

 series of reverberations is heard, and iu 18.6 seconds the sound reaches 

 the bend, returning in 37.3 seconds to the end of the second tubes, 

 having traversed 12.75 kilometers. It is distinctly perceptible by the 

 ear as a single, dull souiul. Accompanying it is a strong puff of air, 

 which at souiewhat greater distances is the only thing perceived. This, 



