100 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



ionth of a centimeter. Indeed, the .author is inclined to 

 think that, on a still night, a sound of this pitch (/J,.), whose 

 amplitude is only a hundred-millionth of a centimeter, would 

 still be audible. 



Mach has devised an apparatus for studying the sonorous 

 waves produced by an explosion. The ball from a pistol 

 perforates two disks of paper which close the ends of a long 

 box, the walls of which are formed of glass smoked with 

 lamp-black. The aerial waves produced by the two suc- 

 cessive ruptures of the paper produce on the glass inter- 

 ference bands, by which the velocity of the ball may be 

 calculated. The results are always lower than those given 

 by the ballistic pendulum, and are brought into accord 

 with these only by assigning 500 meters per second as the 

 velocity of sound. It thus appears that the velocity with 

 which sound travels increases with the suddenness of its 

 production. 



Mercadier has further studied the laws of the vibrations 

 of tuning-forks, considering especially their isochronism with 

 varying amplitudes. Three methods were used: in the first, 

 the amplitude was maintained constant during each experi- 

 ment, but was lessened from one experiment to another, the 

 vibrations being recorded on a rotating cylinder; in the sec- 

 ond, a large amplitude of vibration was given and then suf- 

 fered to die out, the vibrations per second at various times 

 being noted ; in the third, a Lissajous curve was inspected 

 as the amplitude of the fork lessened. The author con- 

 cludes, 1st, that the duration of the vibration period of forks 

 varies with the amplitude and in the same direction; 2d, 

 that this variation, even for amplitudes as great as one cen- 

 timeter, is small, affecting only the second decimal place; 

 and, 3d, that if a certain limit, say four millimeters, be not 

 surpassed, the duration of the period may be regarded as 

 constant. 



The same physicist has published a description of a new 

 form of apparatus for showing optically the resultants of 

 the combination of two rectangular vibrations, by means 

 of which any desired difference of period and of phase can 

 be obtained and maintained. The apparatus consists of a 

 heavy fork vibrating by means of an electro -magnet, and 

 having heavy sliders so as to vary the rate an entire oc- 



