A. M. Mayer—Acoustical Experiments. 269 
Three forks are taken which are supposed to give the same 
number of vibrations in a given time. They are supported on 
india rubber tubing, and are thus insulated. One of the forks is 
now loaded so that it gives two or three beats in a second, with 
one of the other two that are to be brought intu exact unison. 
The interval of time occupied by 20 or 30 of these beats, is_ 
accurately determined by means of a chronograph (one of 
Casella’s registering stop-watches does very well). The interval 
occupied by the same number of beats given with the second 
fork, is now ascertained, and if it differs from that given by the 
first, the quicker. vibrating fork is made to give the same num- 
ber of beats as the slower by loading it with wax. When the 
forks have thus been carefully adjusted, I have had no difficulty 
in projecting the ball, in Exp. 1, at a distance of 60 feet, and I 
believe that it could have been accomplished at a distance of 
100 feet. The ball of cork should be spherical, so that it will 
always just touch the fork, no matter how much it may rotate 
around its suspending thread; which latter should consist of 
only one or two fibers of unspun silk. The cork is rendered as 
smooth as possible and is then varnished: this is important, for 
the varnish gives a firm coating to the ball, without sensibly 
increasing its weight, and is especially useful in covering the 
minute asperities or elastic projections on its surface, which 
otherwise would act as “ buffers” to the impacts of the fork and 
deaden its projectile effects. 
_ The above stated conditions having been obtained, no phys- 
icist will have any difficulty in repeating these experiments. 
machine has been devised by which a uniform motion of 
translation can be given to the forks, and with this I propose 
making a quantitative investigation of the phenomena, using an 
acta essentially the same in its action as the one here de- 
seri 
We may substitute for the suspended cork-ball a light plane 
mirror, held between two stretched vertical fibers, while one of 
its edges touches the fork. The motions of a beam of light 
reflected from the mirror to a screen, indicate most beautifully 
the vibrations of the fork. This ingenious and most delicate 
device for detecting vibrations, is due to Prof. O. N. Rood, of 
lumbia College, N. Y., who first used it in a public lecture, 
delivered in New York, on the 28th of last December. We 
have, however, in our special work, found the image of the pro- 
jected ball more convenient, and sufficiently delicate, for our 
experiments. 
Quantitative relations in the experiments and analogical facts in 
the phenomena of light. 
The UT,, No. 1 fork, makes 256 complete vibrations in one 
second, while fork No. 8 makes 254, giving for the respective 
- 
