PROCEEDINGS OF SOCIETIES. Li? 
tion, and it was this defect that induced Mr. Lealand to introduce 
glass as a reflecting medium. My own impression is that the 
glass being movable, as in Mr. Beck’s arrangement, is an advan- 
tage, but I am unable at present to give any positive opinion. 
Both plans will, I think, be useful; and we are greatly indebted 
for the improvement made on the American plan, and to Mr. Beck 
for having brought the subject before the Society. 
Mr. Bocxerr.—I have worked with both these instruments. 
LT applied myself to Messrs.. Powell and Lealand’s, but my first 
trial was anything but successful. There appeared to be too 
much glare; indeed, so much that I took back the instrument 
and asked that the cause of this might be explained. I was 
informed then that the glass was really parallel glass, and that, in 
all probability, my manipulation would be found to be at fault. 
I studied the matter very closely, until I found that my great 
fault lay in using too much light. When too much light is used 
a glare is produced, and the very best way to get rid of that 
glare is to use just sufficient light for the purpose of illuminating 
the object. I found, by using the Sorby instrument, and getting 
the light just to fill the aperture of the diaphragm at the side of 
the illuminator, and no more, and then stopping it down with the 
next-sized stop, I nearly got rid of the glare, and that often the 
second aperture got rid of it altogether. I cannot say that with 
Mr. Beck’s illuminator I could entirely control the light in the 
same way that I could with Messrs. Powell and Lealand’s. I 
mention this because I think the glare of light is often the cause 
of fault being found with the instrument, when it really lies with 
the parties using too much light. I also observed another import- 
ant tact—that by introducing a small piece of light thin glass 
between the orifice, if there was any milkiness, it was so absorbed 
by the altered nature of the light that really the object was 
pleasant to look upon. 
Mr. Becx.—I should like to say a few words in reply. I have 
found the best mode of proceeding to be as follows :—Place the 
light on the left-hand side, and obtain a distinct image of the 
flame across a portion of the field of view; it is then evident that, 
if you have the illuminating rays in focus at the same time as the 
object, you must also secure the best possible definition. The 
effect of a diaphragm at the side is merely to limit the area of the 
illuminated part, a result which may readily be obtained by 
interposing a condensing lens between the light and the illumi- 
nator. By slightly altering the position of this lens the whole 
of the field of view or any part of it may be illuminated. Mr. 
Beck then sketched the appearance of the fine “tenent hairs” 
on the foot of a fly as seen under this new mode of illumination, 
clearly indicating the same structure as those on some of the 
beetles which have been so admirably illustrated in Mr. Tuffen 
West’s paper on the feet of insects, published by the Linnean 
Society ; and he mentioned, what might not be known to all, that 
the true action of these hairs is still a point of discussion between 
Mr. West and Mr. Backwall. 
