30 THE MICROSCOPE. 
parabola, and D. the diaphragm. On the right hand side, the light 
from the entire aperture of the reflecting surface is represented as 
reaching the object, as shown by the dotted lines; while on the left, 
only the most oblique rays are transmitted through a small hole in 
the cardboard diaphragm. 
The chief objection to this method of illumination is, that the 
central light cannot be obtained, but this, of itself is of no particular 
account as the parabola may be removed from the substage when it 
is desired. 
As to the performance of this arrangement, I can speak in the 
highest terms; the resolution of the diatoms of Miiller’s balsamed 
plate being easily accomplished; and when the full operation of the 
parabola was used the dots of No. 18 showed better than I have 
ever seen them by any other method of illumination. 
When used with dry objectives the effect is simply that of dark- 
ground illumination by very oblique pencils of light. 
GIVE CREDIT: TO WHOM CREDIT IS DUE. 
BY PROF. ALBERT M’CALLA. 
N Page 230 of THE Microscope of December, you copy from 
the Chicago Times’ report of my Presidential address last 
August, before the A.S. M., my brief and modest reference to a 
new form of adjustable nose-piece invented by me, and on page 218 
you describe and illustrate the apparatus itself. Unfortunately, 
however, in this latter reference the name is altered and Mr. Bulloch, 
with most unrefreshing audacity,claims the entire credit of the inven- 
tion for himself and utterly ignoring my name, announces that the 
apparatus has been patented by himself. The contrivance that Mr. 
Bulloch announces as the “Congress Adjustable Nose-piece” is my 
own invention throughout, made, drawn and described by me three 
years ago. Last August I requested Mr. Bulloch to make it up 
that it might be shown and described at the next meeting of 
the A. S. M., and be brought into general use. He agreed to do 
so, and did make it in every essential feature exactly according to 
the sketches and descriptions I gave him last August, at the Chicago 
meeting. I intended sending you a full account of the same, with 
illustrations, in time for the October issue, but a pressure of other 
duties prevented. (I have been rebuilding my house this fall, while 
