594 SCIENTIFIC RECORD FOR 1885. 



of the second fork directly on the screen, he receives it on an oscillating 

 or revolving mirror, which sends it to the screen. If either fork vibrate 

 alone, the curve is the simple sinusoid corresponding to its rate ; while 

 if both are put in vibration the compound curve characteristic of the 

 interval is obtained. If the ratios are exact, the form of the curve de- 

 pends on the difference of phase and is constant. If they are not exact, 

 interference takes place and the beats are seen to have their optical ex- 

 pression. {Am. J. Sci., March, 1885, III, xxix, 234.) 



Felici has suggested the following arrangement for showing Lissajous 

 figures by means of vibrating strings. A piano wire, something more 

 than a meter long, is strung horizontally in such a way that the tension 

 can be varied at will. Upon it is fixed vertically by means of a little 

 cement a card in which a narrow horizontal slit has been cut. Behind 

 this wire a second similar wire is placed vertically exactly opposite the 

 center of the slit in the card. The tension of both cords is so regulated 

 that their vibration ratios are simple. On vibrating them both simul- 

 taneously in parallel vertical planes, so that the two vibrations are per- 

 pendicular to one another, and on throwing a beam of light through the 

 point of intersection, the image on a screen formed by means of a lens 

 shows the characteristic Lissajous curve in black within a bright rect- 

 angle. {11 Nuovo Cimento, xvi, 160; J. Phys.y December, 1885, II, it, 

 557.) 



In order to facilitate the determination of the number of beats given 

 by a vibrating body witb a fork of known pitch, Israileflf has constructed 

 a pendulum the vibrations of which can be regulated to coincide with 

 the beats observed. For this purpose he displaces a weight micromet- 

 rically along the rod of the pendulum, prolonged for this purpose above 

 the axis of suspension. An empirical graduation permits direct read- 

 ing: of the number of vibrations to be added to or subtracted from the 

 number of the vibrations made by the fork in order to obtain those 

 of the sounding body. In Kussia the bells in church towers are fixed 

 and are struck by their tongues acting as hammers. To produce an 

 agreeable effect, the bells must be so tuned that they yield exactly 

 the harmonics of the same fundamental tone. It is for this purpose 

 that the above device was constructed. Isralieff has himself made the 

 tuning forks for comparison. The set begins at 440 vibrations and con- 

 tinues to 880, increasing regularly by 8 vibrations, tuned with great 

 care. To lower the tone the central portions of the bell are turned off 

 on a lathe, and to raise the tone, the peripheral portions, until the 

 proper tone is reached. {J. Soc. Phys.-Chim. Busse, xvi, 1; J. Phys., 

 December 1885, II, iv, 588.) 



In 1879 Mayer devised a method of measuring with great accuracy 

 the vibration periods of tuning forks, the details of which have only now 

 been published. It consists, first, in making the tuning fork, to which 

 an exceedingly fine light style is attached, describe its own vibrations 

 on a revolving cylinder covered with smoked paper ; and, second, in de- 



