2 
Psyche 
[March 
it appears likely that harmonics may be mistaken for the 
fundamental. For this reason, and because of difficulties 
thought to be introduced by the Doppler effect, not much 
attention has been given to this method by later workers. 
The optical method of Wheatstone (1827) was applied by 
Marey (1868) to the study of wing motion. By gilding areas 
of the wing he was able to observe its trajectory in living 
insects held with forceps, and confirmed Pettigrew’s (1868) 
deduction that the wing stroke follows the outline of a 
figure-8. The type of problem for which this method is suit- 
able is illustrated further by the work of Stellwaag (1916), 
who was able thus to observe the differential action of the 
wings in steering. The method cannot be called on, however, 
for the sort of detail available so abundantly in a photo- 
graph, and has the further disadvantage that information 
gained from it must often pass through a stage of subjective 
interpretation before it reaches the record. It permits some 
degree of measurement of the various amplitudes of the 
wing motion, but affords no data as to rate. 
Marey (1868) also introduced the use of the kymograph 
in the study of wing motion. This instrument gives a per- 
manent non-sub jective record, from which it is easy to cal- 
culate frequencies, but is limited in other directions. The 
wing of the insect, used as the recording lever, is of fixed 
radius, and its motion is complex. If undue friction is to 
be avoided, only a small fraction of the arc described by the 
wing tip may be recorded at one time. Insofar as frequency 
measurements are concerned, the results obtained by Marey 
and other students who have used the graphic method agree, 
on the whole, within the limits of normal variation with data 
derived from other techniques. The distortions bulk larger, 
however, where it is desired to achieve a true picture of the 
unhampered motion of the wing. Naturally the kymograph 
may be used only with fastened and not with freely flying 
insects. 
A third technique introduced by Marey and in the develop- 
ment of which his followers have had a large share is that 
of high-speed photography. Theoretically this is the most 
advantageous method for the study of insect flight, but its 
application is difficult. The high rate at which the wings 
are moved, 150-250 beats per second being not uncommon 
