422 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
nicety of adjustment : Mr. Nelson’s, a cone actuated by a milled head on 
the left, and pushing against a spring, fitted only to a few No. 1 Powell 
stands ; a micrometer movement with the milled head at the end of the 
tail-piece, in the large Baker-Nelson model ; and Messrs. Watson’s, a 
lever movement with the 
head placed at the upper 
right-hand side pf the maiu 
stage, in their Van Heurck 
instrument. Working as 
I do with one of Messrs. 
Swifts’ stands, I suggested 
to them the advisability of 
providing a fine substage 
movement for their larger 
instruments, and they have 
carried out and improved 
upon my ideas with their 
usual mechanical skill. The 
movement essentially con- 
sists in the adaptation of 
their well-known “Climax” fine-adjustment to the slide carrying the 
suhstage, but it is actuated by a milled head borne on the spindle to 
which is connected the pinion of 
Fig. 53. the coarse or rack motion ; in 
fact, so far as the arrangement of 
the two milled heads is concerned, 
it resembles the “ Turrell ” stage 
movement. One complete turn 
of the inner head raises or de- 
presses the substago the 1 /125 in., 
so that very small fractions of 
this amount are readily obtain- 
able, and as the two movements 
are close together and move in 
the same direction, manipulation 
is very easy. The “lift” is as 
nearly as possible central. 
I submit this adjustment with 
confidence to those microscopists 
who have felt the want of some such contrivance when working with 
the highest class of optical appliances. 
The Camera Obscura v. the Camera Lucida.* — Dr. Henry G. Piffard 
remarks : — “ In drawing from the Microscope three methods are in vogue : 
(1) The observer studies the subject on the slide, and when he thinks 
he has the outlines and details sufficiently impressed on his mind, with- 
draws his eyes from the tube and commits the mental picture to paper, 
using both eyes in directing the movements of the pencil. (2) The 
observer, looking down the tube with one eye (usually the left), is 
enabled to see the virtual image by a sort of autoprojection delineated 
* The Microscope, xii. (1892) pp. 92-3. 
