ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
869 
(April) of the Journal, Mr. Gifford, in connection with the resolution of 
the Amphipleura, advances an idea which is probably novel to many, 
namely, photomicrography by means of monochromatic yellow light. 
As I have personally worked in this direction for some time, and have 
carried the idea a step farther than Mr. Gifford appears to have done, 
I take the liberty of bespeaking the courtesy of your pages. I will 
briefly relate the main facts which led me to tbe processes I now employ 
in photomicrography, and which in low power work give me results 
vastly better than those at present in vogue, although in high power 
work I have not as yet observed the same advantages. 
In 1873 I purchased a No. 4 Hartnack objective (about 1/2 in.). It 
was a glass of quite moderate angle but otherwise good of its kind. 
Employed in photomicrography, using the then customary collodio- 
iodide wet plate, the results were not satisfactory. About 1878 I 
purchased a Wales 4/10-in. Ang. Ap. 90°. This lens was and is still 
a remarkably good glass to look through, but it utterly failed to give a 
satisfactory result when used photomicrographically at the time of 
purchase. Five years ago I tried it again, using the now customary and 
ordinary gelatin-bromide dry plate. The results were disappointing. 
About four years ago I became interested in the so-called orthochromatic 
plates, and as they were not at that time an article of commerce in this 
country, was obliged to prepare my own, and succeeded in preparing such 
as were equally sensitive to blue, green, and yellow, and almost wholly 
insensitive to violet and ultra-violet. I also made such as were remark- 
ably sensitive to yellow, but hardly at all to the other colours. The 
methods employed were published by me a few years ago in ‘ Anthony’s 
Photographic Bulletin.’ The commercial plates now obtainable in this 
country are markedly sensible to yellow, less so to blue, and still 
less so to green. On the whole they are of better quality than similar 
plates of English manufacture that I have tried, though not equal to 
some Yogel-Obernetter-Perutz plates that I once had the opportunity of 
using. 
About ten months ago I asked Mr. W. Wales to make me some 
low power objectives specially corrected for photomicrography. He 
did so, but the lenses did not satisfy me, and I retained but one of them. 
I subsequently asked him to make me a 1/4 in. When he brought the 
lens he said, ‘ I have put this in a rough mounting in order that you 
may look through it as it is before I finish its correction for photography, 
as I shall undoubtedly impair its visual performance to a certain extent.’ 
He further said, ‘ I think it is the best 1/4 in. of its angle (75°) I have 
ever made.’ On visual examination (Podura) the lens left little to be 
desired, but being curious to see just how far ‘ off’ it was photographi- 
cally I made a negative using a commercial (isochromatic) plate. The 
result was a gratifying surprise. On reporting the matter to Wales he 
said, { I do not understand it, the lens in the condition in which I gave 
it to you ought not to have photographed so well.’ For comparison 
I photographed the same scale with a Powell-Lealand 1/4-in. water- 
immersion N.A. 1 • 26 which I have owned for several years. The 
resulting negative was not equal to that made with the lower angle 
Wales. 
I believe it is generally maintained, and I think with justice, that 
