266 E. J. SPITTA ON SOME EXPERIMENTS RELATING TO 



a monochromatic screen ; for when such was removed, all trace 

 of the multiple-image effect was removed also. The phenomenon 

 was believed to be due to pin-hole effects. A friend, however, 

 suggested that perhaps the multiple-image effect in the diatom 

 might not have been due to the cause assigned, but may have 

 arisen from some of the natural covering of the diatom not 

 having been completely removed in the cleaning, and which, 

 assuming a lenticular form, had produced the appearance in 

 question. To solve this riddle I obtained some perforated zinc 

 and photographed it. The operation was repeated several times, 

 until the image of the perforations became so small as to 

 almost require a lens to see them. This artificial cornea was 

 placed on the stage of the microscope, and a little cross on a 

 piece of glass placed beneath — in fact the same arrangement as 

 that employed when the microscopist show's the multiple effect 

 with the real cornea of the insect. There was at once revealed 

 a little cross in each tiny hole of the photograph of the zinc, 

 similar in fact to that seen in each facet of the insect's eye. 

 There could be no doubt here that the phenomena were entirely 

 due to pin-hole effects, and this led to the idea now suggested that 

 it is possible that the multiple images produced by the insect's 

 eye arises from precisely the same cause. As I have already 

 said, these experiments were performed some years ago; hence 

 a considerable time has elapsed for the consideration of the 

 matter. But the longer I think upon it, the more the assumption 

 seems worthy of acceptance ; and it is in consequence of this 

 that I have at last thought the moment ripe for bringing the 

 matter before the Club, so as to have the benefit of the opinion 

 of the members. 



It would seem that if the facets of the cornea were considered 

 as nothing but little holes — filled, it may be, with some non- 

 refractive material — all the difficulties about the focussing 

 arrangement are at once swept away ; for it is well known that 

 every image is to a more or less degree in focus with a pin- 

 hole. This would seem to imply that a very perfectly defined 



