836 
PROCEEDINGS OF THE SOCIETY. 
Mr. J. Mayall, jun., created some amusement by reading from 
‘Nature’ an advertisement of a newly-invented Microscope, and exhi- 
biting the article to which it referred, with comments upon his experience 
as a purchaser. 
Mr. Andrew Pringle having sent to the meeting two photographic 
prints showing the flagellum of Bacterium Termo, they were handed to 
Dr. Dallinger with a request for his opinion. 
Dr. Dallinger said that there was no doubt that the flagellum was 
quite clearly seen in these photographs, but it was, as indeed was 
always the case in photographs, prolonged wonderfully, and presented 
an extremely rotten or imperfectly defined edge. Prof. Abbe had 
taught them that in looking at an object^' so minute as this, they 
were really looking upon a diffraction image of it rather than upon the 
thing itself, and that this image was always seen as something larger 
than the real object. How this affected the photograph he was unable 
to tell, from want of a thorough knowledge of the process, but he knew 
that when looking at such an object with any power from 1/8 in. up to 
1/50 in. with a numerical aperture of 1*47, a clear and sharp definition 
was obtained of the flagellum, which appeared to be about one and a-half 
times the length of the body. Here in the photograph it extended a 
long way beyond this, giving him the impression that there might be 
two interlocked. At any rate, there was great skill shown in the pro- 
duction of these pictures. 
Prof. Bell said no doubt the Fellows of the Society had carefully 
read an article in the last number of the Journal on the Retinal Image 
of the Insect Eye, in which mathematical formulae were given and 
woodcut illustrations to show the nature of the image produced by the 
compound eye of an Insect. Prof. Exner, the author of the memoir noted, 
had sent to Dr. Sharp a photograph of the image so produced, and 
Dr. Sharp, in the most friendly manner, had placed it at Prof. Bell’s 
use for exhibition that evening. It would be remembered that, as a 
result of his investigations, Exner arrived at the conclusion that a single 
erect image was thrown upon the retina of the compound eye of an 
insect. From time to time various theories have been advanced, but 
that of Johannes Miiller, that patches of images on a kind of mosaic 
plan w T ere produced, seemed to still “ hold the field.” The photograph 
exhibited shows — and its evidence is corroborated by mathematical 
calculation — that it is perfectly certain that the retina of an insect does 
receive a single image just as we ourselves receive a single image on 
the retina of each of our eyes. In our own case w r e have to learn rightly 
to estimate the position of objects, for the image which we receive is 
inverted, but in insects it seems that the image which is received is 
single and is also erect. In that it is single it is the same as our own, 
but in that it is erect it differs. In the taking of the photograph the 
eye of the insect was pointed towards a window — the letter R was put 
on one of the window-panes, and there was a church outside. In the 
photographed image the letter R is plainly seen, and the church is 
visible. The photograph was handed round for inspection. 
