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THE CANADIAN ENTOMOLOGIST. 



spectrograph to obtain satisfactory negatives of the various species of 

 fire-flies. The photographing was done in a dark room. Over 150 

 negatives were taken, over 56 hours being spent in holding the insects in 

 place. The plates, being sensitive to red light, were developed and fixed 

 in a perfectly dark room. The numerous details in the work will be pub- 

 lished in the complete paper. 



Prints from negatives of the light of Photurts pemisylvanica and of 

 Fhotiiius pyralis are given in fig. 23, from which it is evident that the light 

 of the Photinus py rails does not extend so far into the blue (A= .5015/x) 



Fig. 23. — a, spectrum of "4 Watt" carbon glow lamp ; b and d, spectrum 

 of fire-fly, Photinus pyralis ; c, spectrum of fire-fly, Photuris peunsylvanica ; 

 d, helium vacuum tube spectrum, used for comparison. 



as, and that it extends farther toward the red (A= .6678/x) than does the 

 light of the Photuris peunsylvanica. 



In addition to the negatives of the fire-fly light, a series of photo- 

 graphs (see fig. 23), were obtained of the spectrum of a standard compari- 

 son lamp (carbon glow lamp operated on four watts per candle) when 

 exposed for 2, 4, 6, 8, 12, 20, 30, 60, 120 and 240 seconds. 



The "densities" or 'blackening" of the photographic plates were then 

 measured by means of a Marten's polarization photometer, mounted on a 

 small comparator, in such a manner that strips 1.5 high and i mm. long 

 were compared against the clear unexposed plate. These "densities," i.e., 

 the amount of light absorbed, were then plotted to scale, as indicated in 



