4 
Psyche 
[March 
light, which was not dependable, or in regard to control of 
the frequency, which was unwieldy because of rotational 
inertia, etc. No difficulties of this sort are met with in the 
instrument under discussion, in which the flash-frequency of 
a neon or other low-pressure-filled bulb is controllable in- 
stantly by an adjustable electric oscillator. The instrument 
as supplied operates on 110 V 60-cycle AC, and gives direct 
scale readings in RPM over a range of 600-14,400 cycles per 
minute (10-240 per second). Values above and below these 
limits may be calculated easily from harmonic relationships. 
The accuracy is within ±1.0% over the full range. 
The motion of an insect’s wings is fundamentally a cyclic 
phenomenon, and may therefore be studied by this means. 
In theory one may place any flying insect before the instru- 
ment and by suitable tuning either “stop” the wings com- 
pletely at any phase in the cycle or permit the cycle to 
proceed slowly through its several phases while observations 
are made. How fully these desired conditions may be at- 
tained in practise varies considerably with different insects, 
but, given appropriate treatment of the specimens, the 
theoretical expectations may be realized very satisfactorily. 
Rates may be determined quickly and easily. 
Study of the complex motions of the wings is more exact- 
ing. Here results depend partly on the operator’s patience, 
since the problem is largely one of inducing the specimens to 
fly steadily and for longer intervals. Favorable responses 
can be had in the majority of cases, and are well worth the 
effort, for the details of the wing motion are displayed with 
a clarity that is far beyond that of any photographs so far 
published. 
The most evident disadvantage of the method is that, like 
other visual techniques, it gives no permanent record beyond 
the notes of the observer. In respect of rate determinations, 
this objection is less forceful, since one simply tunes to 
synchrony with the wing frequency, thus obtaining a single 
standing image, and reads the figures from the dial. Refer- 
ence to adjacent harmonics quickly settles any doubt as to 
whether one has been observing the true fundamental or one 
of its submultiples. 
Because of the natural variation in rate, it is often difficult 
to retain a standing image over any extended period, though 
