6 
Psyche 
[March 
effect upon many insects, so that these tubes have not been 
as useful in the study of free flight as had been hoped. 
Whether this is due to some peculiarity of the spectrum, or 
to an effect of flicker at the higher intensities, which is lack- 
ing with the neon bulb, has not been determined. Certain 
moths are sensitive to noise, and respond adversely to the 
high-voltage crackle from these tubes as well as to the 
quality of the light. Still it has been possible to take read- 
ings on the wing rate of these and other insects flying freely 
in a room 12' x 15', and observations on specimens confined 
in jars and other containers are often productive. The 
brighter bulbs have also been used to advantage in studying 
specimens held in fixed position. At present it is not pos- 
sible to obtain tubes of this sort which will operate at fre- 
quencies much above 100 per second. In connection with the 
problem of lighting, it may be remarked that, no matter how 
perfect it may be made, there will always be the natural 
variation in wing frequency to deal with, as well as the 
limitation set by what the human eye can observe in a small 
object traveling rapidly through space. 
Where specimens held in fixed position are to be studied, 
the technique of fastening them is important. A discussion 
of the problems this introduces would lead beyond the limits 
of this article, and must be deferred to another occasion. 
Finally, one additional limitation of the stroboscopic 
method should be noted. At rates well below the fusion fre- 
quency for the human eye, there is, as might be expected, a 
disagreeable flicker. This is especially objectionable when 
one is observing through the binoculars. Fortunately the 
wing rate of most insects is high enough so that this draw- 
back is of minor consequence. The writer finds observation 
not uncomfortable at frequencies as low as 20 or 25 per 
second, where detail, such as motions of parts of the thorax, 
is to be studied. Direct rate readings are possible down 
to the limit of 10 per second, or may be taken in higher 
multiples if this seems preferable. 
In concluding this criticism of the stroboscopic method, 
one may point again to the great advantage of being able to 
make direct visual observation of the motions of flight, at a 
rate determined by the observer, and also to the large num- 
ber of observations that can be made within a limited time. 
