10 
MR. H. M‘LEOD AND LIEUTENANT G. S. CLARKE ON THE 
Bowed every 20 seconds. 
Temp. 
Bowed every 5 seconds. 
Temp. 
512-470 
16-1 
512-460 
16-2 
512-460 
16-25 
512-452 
16-25 
512-460 
16-3 
512-456 
16-4 
Mean 512-463 
16-22 
512-456 
16-28 
(These numbers are not corrected for the rate of the clock ) 
The effect of frequent bowing, therefore, appears to be to make the fork vibrate a 
little more slowly, the diminution of rate being ‘00137 per cent. The fork was one of 
Kcenig’s, and of stout metal ; lighter made forks may be affected to a greater extent. 
Lissajous found that no change of form was exhibited by his figures when the forks 
were bowed (‘ Comptes Rendus,’ 1855, xli., 816); although a different result was 
obtained by Poske (Pogg. Ann., 1874, clii., 449), who observed that the increase of 
amplitude produced by bowing seriously altered the rate of vibration. He, however, 
seems to have used a vibroscope, in which the ends of the prongs were weighted by a 
lens and counterpoise.* We have recently endeavoured to settle this question in 
another manner. The microscope being placed horizontally, a 256 fork was fixed ver¬ 
tically at the focus of the objective, and another fork was placed horizontally in such a 
position that an image of its edge was thrown by the lens in the substage on to 
the edge of the vertical fork. In this way the Lissajous’ figure was seen in the 
angle made by the two images. No change of phase was perceptible on bowing either 
of the forks. Where two 60 forks were tested in a somewhat similar manner, a 
change of phase was seen ; but one of these forks is thin in comparison with its length, 
and the prongs are weighted by a lens and counterpoise. It is evident, however, that 
the unskilful bowing of a light fork may alter the phase, by first damping and then 
re-starting the fork. 
2. Effect of the variation of amplitude. 
To determine the effect of different amplitudes, the scale in the eyepiece of the 
microscope was placed horizontally, and the amplitude kept as constant as possible by 
suitable bowing. Four experiments were made, each of five minutes’ duration. In 
the first and third, the movement of the end of the prong was about ‘37 mill i m. ; in 
the second and fourth, about T5 millim. The results are as follows :—- 
Large amplitude. 
Temp. 
Small amplitude. 
Temp. 
256-277 
16-2 
256-275 
16-25 
256-273 
16-4 
256-274 
16"45 
Mean 256‘275 
16-3 
256-2745 
16-35 
* Katser, also, in liis determinations of the effects of temperature, employed weighted forks (Ann. der 
Pkysik u. Chemie, 1879, N. F. viii. 444). As far as our experiments go, such forks seem to behave, in 
many respects, differently from those of the ordinary form.—(Note added December 31, 1879). 
