292 
Transactions of the 
fMonthly Microscopical 
L Journal, Dec. 1, 1869. 
chromatic light obtained by reflecting the direct rays of the sun 
from a hehostat upon a mirror, by which they were thrown through 
a cell filled with a solution of the ammonia sulphate of copper, upon 
the achromatic condenser. As an achromatic condenser I substituted, 
for that belonging to the large Powell and Lealand stand of the 
Museum, a |th of an inch objective of 148° angle of aperture, and 
used it without a diaphragm ; obliquity of light was obtained by 
moving the centering screws of the secondary stage. 
I also obtained satisfactory resolution of the nineteenth band, 
with the same lens, by using for the illumination violet light, 
obtained by throwing the violet end of the solar spectrum produced 
by a large prism upon the achromatic condenser used as above, 
and subsequently by shifting the prism got successful resolution of 
the nineteenth band with blue, green, yellow, orange, and red light. 
These results I had the pleasure of exhibiting to Dr. Barnard and 
several others. 
As for other lenses, carefully tried on the same plate, I obtained 
the following results : — 
The Jth of Wales and the ^^th and sVth of Powell and I<ealand, 
all dry lenses, resolved the fifteenth band, but not the sixteenth. 
An immersion yVth by Wales resolved the sixteenth band, but 
failed to go farther. An immersion sVth by Wales resolved the 
seventeenth band, but failed to go farther. A Hartnack immersion 
No. " 11," belonging to President Barnard, also resolved the seven- 
teenth band, and faHed to go farther. 
A Tolles' immersion ^th, just constructed for Dr. J. C. Eives, 
of this city, resolved the fourteenth band, but failed to show the 
true lines on the fifteenth. This result with the Tolles' immersion 
^th corresponds with the results very recently obtained with a 
Tolles' immersion Jth, just received by my distinguished friend, 
Mr. W. S. Sullivant, of Columbus, Ohio, who wrote me May 25th 
of the present year : — " The immersion lens you inquired about, 
which Tolles sent me, was marked ^th, but was only a strong -^-th 
English standard. The utmost it could do was to show true lines 
on the fourteenth band." 
These results confirm the opinion expressed in my former 
article, that the lines claimed to have been seen, but not counted, 
in the nineteenth by a Tolles' immersion ^th were spurious lines, an 
opinion to which still greater weight is added by the following 
result : — A Tolles' immersion yVth of 175° angle of aperture was 
received at the Museum, May 26th, from Mr. Charles Stodder, who 
stated in his accompanying letter, that it might be regarded as a 
fair sample of Mr. Tolles' work. With this lens, after numerous 
careful trials, I was unable to see the true lines beyond the six- 
teenth band. 
It will be seen, then, that in my hands the best definition was 
