1939] 
Study of Insect Flight 
5 
constant frequency over an interval as long as one minute 
has been observed not infrequently in Drosophila . In deter- 
mining rates, this is again of no particular disadvantage in 
most cases, for here the limits of variation are the significant 
feature and may be measured quite accurately. Where ob- 
servations of wing motion as such are to be made, however, 
it is of importance to know whether or not the apparent 
motion has the same sign as the true motion. For example, 
the wings of a noctuid moth during the downstroke show a 
marked upward curvature of the flexible tips. If the strobo- 
scope be tuned to a frequency slightly above that of the 
wings, there will be a slow apparent motion in reverse of the 
true motion, and the wing tip will then seem to be bent 
upward during the upstroke. Such incongruities may be 
less patent in the motions of a smaller or more stiff -winged 
insect, so that caution is necessary. This is particularly so 
of insects with a very variable rate, whose true frequency 
may be now to one side and now to the other of the setting 
on the dial. 
Transient motions, for example those involved in starting 
or in stopping flight, are beyond the scope of such a method. 
Here, as in many other instances, the ultimate recourse must 
be the motion-picture camera. 
A further weakness of the instruments obtainable at 
present is that the intensity of the neon bulb is rather low. 
This means that specimens must be placed close to the 
source, and outside illumination cut off or reduced to a 
minimum. In theory it should be quite possible to observe 
with stroboscopic light the motions of an insect flying freely 
in a room ; practically this ideal is difficult to attain. Even 
with completely adequate lighting such methods could not be 
satisfactory with the smaller species. With larger forms, of 
the size of Leucania unipuncta Haw., for instance, they may 
be useful, once the essential improvements have been made. 
With the cooperation of Professor Edgerton, of the 
Massachusetts Institute of Technology, the writer has been 
supplied with additional equipment, including tubes of 
higher intensity. These give a bluish-white light which is 
suitable for certain types of photographic work. Photog- 
raphy with the neon tubes is out of the question. Unfor- 
tunately the bluish-white light seems to have an inhibitory 
