ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
649 
& Sons, exhibited and described a new student’s Microscope which he had 
devised. 
The late Mr. John Mayall, in introducing it to the President, said 
the special point was in the application of a screw movement for the 
substage adjustment. He thought it a very economical and excellent 
way of applying the focusing arrangement to the substage, and it appeared 
to him most happily chosen for convenience, and would certainly com- 
mend itself to notice. It seemed to him that Messrs. Johnson had 
undoubtedly “ scored 1 ” by bringing out this screw-focusing arrange- 
ment for the substage. 
This instrument has been constructed with a view to supply the 
student in the higher branches of research with a suitable Microscope at 
a moderate cost. The foot (fig. 70, A) is of the horse-shoe form, and 
sufficiently weighty to insure steadiness when used in a horizontal 
position for photomicrography. 
The patented screw substage adjustment consists of a screw placed 
in the axis of the substago and tail-piece, which is actuated by a milled 
head nut, slightly projecting at A ; this being readily at command gives 
great facility for raising or lowering the substage, and delicately focus- 
ing the condenser, &c. The substage carrying an Abbe condenser with 
iris diaphragm and mechanical centering arrangement is mounted on a 
substantial tail-piece and slides in dovetailed fittings. The substage with 
its fittings (when in use) is fixed to the Microscope, and is free from lateral 
motion ; by a simple arrangement of a clamping screw it can be readily 
removed or replaced (see fig. 70, B) and is, as regards durability, far 
superior to the pivoting system. The mirror can also be removed for 
direct lights if required. 
The fine-adjustment is on the differential screw principle insuring 
delicate focusing for high powers, and the coarse-adjustment on the oblique 
rack-and-pinion system, giving equality and smoothness of motion, the 
body being supplied with a draw-tube, and marked for English or 
Continental objectives. 
A great advantage is gained by this position of the substage adjusting 
knob, as in addition to its being readily at command, all liability of 
tilting the mirror or disarranging any of the under-stage apparatus is 
avoided, “ accidents ” which often happen where it is necessary to feel 
for the adjustment when placed beneath the stage. 
A College Microscope.* — Dr. W. H. Seaman observed : — “ It may 
be remembered that in March 1888, Science published an article by me, 
maintaining the excellence of American Microscopes. The train of 
thought inspired by that article led me to make working drawings of an 
instrument with some novel features. These were shown to a few friends 
at Columbus, and were unfortunately lost from my coat-pocket at Buffalo. 
I did not have time to reproduce them till recently, and hoped to have 
the instrument itself here, but it is not quite done. 
The figure (fig. 71) shows the features which are essential, in my 
judgment, to a good College Microscope. It will also be well adapted 
to the average professional man and amateur. A tripod base, rather thin, 
* Proc. Amer. Soc. Micr., xii. (1891) pp. G7-8. 
