PHYSICS. 245 



siau well. The pressui'e was read oil" on the graduatetl suspending wire. 

 To determine the volume, the inside of the piezometer tulx^ was gilded, 

 and the height to which the mercury rose in it was show n by the removal 

 of the gold. The measurements were carried on with nitrogen to 182 

 atmospheres. Cailletet has also studied the effect of pressure on gaseous 

 mixtures, and has described a method by which a pressure of 1,500 at- 

 mospheres may be measured to within one-half of 1 per cent, of its true 

 value. — {J. Phys.y viii, 267 ; ix, 192 ; Ann. Cliim. Fhys., V, xix, 380, 

 March, 1880.) 



ACOUSTICS. 



Carmichael has devised a revolving jet to be used withKoenig's mano- 

 metric capsule for the purpose of showing sonorous vibrations in class 

 instruction. A tube bent at right angles and tipped with a jet is sur- 

 rounded at its extremity by a second concentric tube also bent at right 

 angles, but in the opposite direction, so that the two bent parts are in 

 the same line and form an axis about which the jet revolves. A mica 

 cylinder incloses the flame, which is that of ordinary gas, enriched, if 

 necessary, with benzene and fed with oxygen. The gas tube is in com- 

 munication with a Koenig capsule, so that the flame is thrown into vi- 

 bration by means of it. On rotating the jet by a multiplying wheel 

 a brilliant ring of light appears, which is broken uj) into saw-teeth by 

 sounds.— (Am. J. Set., Ill, xLx, 312, April, 1880.) 



Schwedoff has described a simple apparatus for studying the vibra- 

 tions of cords, which consists in an electric vibrator like that in use for 

 bells. The cord is attached to the armature at one end, the other being 

 fastened to a movable clamp which slides along the top of a blackened 

 board divided into a nmnber of equal divisions. To the clamp tlie cord 

 is attached by a screw, by which its tension may be regulated at pleas- 

 ure. — (fJ. Pliys.^ viii, 23, January, 1879.) 



Mercadier has exhibited in Paris a vibration micrometer for accurately 

 determining the vibration-amplitude of tuning-forks and other vibrating 

 bodies. A small piece of thin white paper bearing a fine black line is 

 fastened to the body whose vibrations are to be measured. If this line 

 is upright it will present, when caused to vibrate, the appearance of a 

 pale gray parallelogram, the persistence of the visual impression being 

 perfectly definite for the extreme positions of tbe vibration. To ascer- 

 tain the amplitude of the vibration, all that is necessary is to measure 

 the apparent width of this minute parallelogram in a direction at right 

 angles to the axis of symmetry of the oscillation. To increase the pre- 

 cision, the reference line is set, not peri)endicular to the direction of the 

 movement, but inclined to it at a small angle. A fine scale of lines is 

 made upon the paper parallel to the direction of the movement and a 

 millimeter distant. The width of the parallelogram is thus read off 

 along a straight line, which makes a small angle with its sides, thus 

 giving the quotient of the amplitude sought by the tangent of a small 



