262 J. J. Woodward on Photographing 
dispensed with. This proposition, which has been adopted by 
many other writers, appears plausible, but a little consideration 
will show it to be quite erroneous. 
Every one knows that a good objective must be free from 
spherical, as well as from chromatic, aberration. Of course the 
use of monochromatic light disposes of the chromatic trouble. 
Not so with the spherical aberration. Now this aberration, like 
consideration, t ' 
he sees is left to a happy chance in the selection of his objectives. 
For even those makers who profess to prepare objectives 
with the problem. If they would’ test their objectives, while , 
ight, we should have better results; 
for photography. "It is only necessary to test their performance 
when illuminated by sunlight, which has passed through an 
ammonio-sulphate cell. Now it fortunately happens that the 
mto consideration the principles involved in the foregoiig 
remarks, 
~ condensing lens above described, This lens, it will 
tated 
us. 
ne convergent pencils proceeding from the first let 
ia and a burning 
