28 Eeliosiatfor PJiotomicrograj>ky, ['^^jt^rn^fX'i^T^^' 
place, did not suit well for my narrow window-ledge, facing S.W., 
at wLicli it had to be used, but led to the plan of stand noted in the 
accompanying sketch, which is firm and portable. To this arrange- 
ment I have since appended the little cubic box as given by Dr. 
Curtis, it being easier to set than the four pointers I had originally 
adopted. 
The arm carrying the second mirror m 2 was at first attached 
to the firm upright piece at the shutter end of the camera baseboard, 
but from the length needed, 20 inches, to give the light reflected 
from the first mirror the necessary horizontal direction, centrally 
with the microscope, it was liable to vibration under a gentle wind ; 
hence it has been mucli shortened and fixed to the under- surface of 
the circular base, h. The clockwork of an American clock is removed 
from its case and set in a rectangular block of teak,* united at its 
lower end by a hinge-joint to the upper surface of a stout circular 
base, h, which carries a short central pin. Fig. 2, from which is sus- 
pended a bob or plumb line. The back of the clock reclines against 
and is fastened to one surface of a block, c, cut to the angle of the 
latitude of the place and fixed over the central line of the circular 
base. On the upper part of the clock-case is screwed a stout brass 
plate, d, turned up sharply each end at right angles, and pierced 
with two centrally opposite apertures, through which passes the 
rod, e, carrying at its upper part a grooved wheel, /, divided into 24 
divisions 12 and 12, and subdivided into quarters, and at its lower 
end the crutch which holds the mirror m 1, one side being prolonged 
to carry the little cubic box, as suggested by Dr. Curtis, which 
rotates on a clamping pin. These parts are supported by two 
friction rollers, gi, resting by their bevel edges on the lower plate 
of the doubly right-angled piece of stout brass plate, and turn easily 
by an endless band carried over the wheel /, and a wheel half the 
size, fixed on the arbor of the hour-hand of the clock. On the upper 
surface of the circular base h is fixed a square compass box h ; from 
the lower surface of beneath the mirror m 1, is screwed a stout 
plate bent at a right angle, and slotted to allow, by clamping, of 
exact adjustment of the arm i, that carries the mirror m 2, the arm 
being pierced at the farthest end to admit the central pin of the 
mirror-crutch or support which, passing through it, is beneath pro- 
vided with a wheel and an endless band carried over a second wheel 
with a milled head, j, fitted for rotation at the opposite side of h. 
By these the mirror, m 2, rotates in the horizontal plane. 
From the under-surface of h hangs a short stem with crutch and 
block, h and Fig. 3, through which runs a steel rod, attached at 
one end to a lever arm connected with the mirror, by it a vertical 
motion is obtained. A small index point is fitted at I. This com- 
pletes the hehostat proper, which, for use, is fixed by the central pin 
* A brafcs box is preferable, or one made of zinc. 
