Vebrations of Solid Bodies. 127 
stancy will then, on the other hand, be the evidence .of perfect 
unison. If the forks are not exactly in unison, fig. 1 will, as 
stated, after some time change into fig. 2, and the number of 
seconds necessary for this change will measure the interval re- 
quired by one of the forks in gaining or losing half of a com- 
plete vibration. dee 
without rising. With this limited aperture, the light from a 
white cloud answered quite well. 
If the forks differ by an interval of an octave, an almost 
equally distinct and well marked figure will be produced, such 
as is seen in figs. 4 and 5, which represent the characteristic 
appearances in this case. This fig- 5: 
ure is quite as useful for purposes ; Dd A 
complicated figures are given by 4 q 
i t 
double octave. It is a little more difficult to distinguish a 
Tuning-forks and vibrating cords.—From the foregoing it evi- 
dently is easy with this method to bring a vibrating string into 
unison with a given tuning-fork, or to adjust it so that the in- 
terval shall be a quint, octave, twelfth or double octave, above 
