1939] 
Study of Insect Flight 
3 
among the Diptera and Hymenoptera, fixes the length of 
exposure, and the duration between successive exposures 
for motion pictures, at exceedingly low limits. To obtain 
adequate illumination at such frequencies becomes a very 
real problem, which is intensified by the small size of many 
species. Added to the photographic difficulties are those of 
posing the often unwilling specimens. Under these condi- 
tions, the method proves expensive in time, film and appa- 
ratus, — yet the results which it promises serve amply to 
justify continued efforts toward its perfection. The extent 
to which the obstacles mentioned have been overcome at 
present may be gauged by reference to the fine reproductions 
in Magnan (1934). 
With the more evident merits and disadvantages of these 
several methods in mind, we may proceed to discuss the 
stroboscopic technique. The stroboscopic principle has been 
the basis of most of the attempts at high-speed photography, 
but Oehmichen (1920) appears to have been the only worker 
who has previously made much use of the stroboscope for 
the visual study of insect flight. With the stroboscope, 
cyclic motions may be made to seem to stand still (and to 
proceed slowly forward or in reverse) no matter what the 
actual frequency may be. All that is necessary is an inter- 
mittent source of light tuned to synchrony (or near syn- 
chrony) with the motion to be observed. In Oehmichen’s 
apparatus light was provided by electric discharge across a 
spark gap or through a Geissler tube. Frequency could be 
synchronized automatically with that of the wings by an 
ingenious arrangement which allowed air currents produced 
by the wing to open a very light key in the primary circuit 
at a given phase in each beat. If a variable control of fre- 
quency was desired, this key was replaced by a rotary inter- 
ruptor, the speed of which was regulated by a potentiometer. 
With this apparatus Oehmichen made visual and photo- 
graphic observations of much interest, but neither his re- 
sults nor his method have received much attention since 
their publication. 
The recent development of the Edgerton stroboscope 
(Germeshausen and Edgerton, 1937) should give a new 
impetus to studies along this line. Earlier stroboscopes have 
suffered from shortcomings, either in regard to the source of 
