36 
Dr. Maddox^ on Photomicrography. 
over a second reel^ which has a sliding motion between its 
points of support to accommodate itself to the play of the 
rack ; from this pulley is passed another band which is en- 
gaged in the groove of the milled head of the fine adjustment. 
This is exceedingly sensitive, worked- by rotating any part 
in the length of the rod, or by its handle at the opposite end 
of the base board, beneath which it is yjlaced to be out of the 
way and not likely to injure the face of the objective by any 
accidental mismanagement. Or the same action is equally 
gained by attaching to the arm from the rack carrying the 
tube or body of the microscope a vertical slip of stout brass 
plate, which passes through the slit in the board, and is 
pierced near its end with an even aperture, in which works a 
double-coned pin, screwed into the centre of the end of the rod 
carrying the reel. An open oblique slit between the upper part 
of the hole and one edge of the strip of brass permits the rod 
being easily removed or placed in its bearing. A band passes 
from the reel on the rod over the groove in the milled head 
of the slow motion. In this method the rod beneath the board 
follows the play of the rack. That there should be no slip, 
the reel on the rod is covered with a piece of vulcanized 
india-rubber tubing. The convenience of being able to act 
on the fine motion at a distance from the stage is very 
great, the focus being under immediate inspection, and the 
eye likely to be kept a less time exposed to the action of a 
bright glare. 
To meet a difficulty very often present, the object not lying 
in parallel plane with the objective, the position of the focuss- 
ing screen being supposed to remain always parallel with it, 
I devised a small adjusting stage. It consists of two thin 
plates of brass of any convenient length and width, pierced 
in the centre with an aperture sufficient for the size of any 
object likely to be used; the under plate is slightly shorter 
than the upper by the width of a thick strip of brass at each 
end, and to these are screwed four flat springs, which, by em- 
bracing the under plate, keep the plates together. They are 
separated by four conically pointed tangent screws, w^orking 
in these strips near the corners ; the conical points, acting on 
a bevelled edge in the upper surface of the under plate, 
force the top one to lift at every angle from the centre, thus 
elevating the object on it. The whole is attached for use to 
the central aperture of the stage of the microscope by a 
ring collar, which thus alFords a means of rotation of its own, 
if required. 
The carrier for the achromatic or other form of condenser 
is attached to the under surface of the stage, as I prefer in 
