EXPERIMENTS WITH ELECTEIC LIGHT. 201 



object, I prepared some nests 12 inches long by 6 inches 

 wide; and Mr. Cottrell kindly arranged for me at 

 the Eoyal Institution on the 29th of June, by means of 

 the electric light, two spectra, which were thrown by two 

 glass prisms on to a table at an angle of about 45". 

 Each occupied about 6 inches square, and there was a 

 space of about 2 inches between them — that is, between 

 the red end of the one and the violet of the other. 



Experiment 1. — In one of the spectra I placed a nest 

 of Formica fusca, 12 inches by 6, containing about 

 1 50 pupae, and arranged it so that one end was distinctly 

 beyond the limit of the violet visible to us, and all but 

 to the edge of the green given by thalline paper, and 

 the other just beyond the visible red. The pupae at first 

 were almost aU in or beyond the violet, but were carried 

 into the dark space between the two spectra, the bright 

 thalline band being avoided, but some pupae being 

 deposited in the red. 



ExperiTnent 2. — I then tried the same experiment 

 with a nest of Lasius niger, in which there were many 

 larvae as well as pupae. They were all at the commence- 

 ment at the blue end of the nearer spectrum. The 

 larvae were left by themselves in the violet, while pupae 

 were ranged from the end of the green to that of the 

 red inclusive. 



Experiment 3. — Arranged a nest of L. niger as 



before ; at the commencement the pupae and larvae were 



much scattered, being, however, less numerous in the 



violet and ultra-violet rays. Those in the ultra-violet 



15 



