60 PHOTO-MICROGRAPHS. 
around the grooved head of the fine-adjustment 
screw, is directed by pulleys attached to the frame- 
work above the microscope, and the spool or key 
by which movement is effected is attached to the 
wooden frame of the movable screen. This ar- 
rangement is more convenient than is that of 
the long-jointed rod, and the control of the fine 
adjustment is perfect at any position of the screen. 
Moreover, the focusing appliance is always ready, 
and at the same time is out of the way, as the cord 
passes from the microscope to the screen above 
the level of the operator’s head. The advantage 
of having the floor clear in a small dark room 
will be appreciated by those who have done much 
work in such a locality. A smooth piece of two 
by four scantling, of proper length, will answer 
very well to support the movable screen. 
When the design is to work zthout a heliostat, as 
is strongly recommended to beginners, it is not 
essential that a window having a southern ex- 
posure be selected, and the window-fixtures are 
simplified to a shelf for the microscope and some 
contrivance for excluding light, except such as 
comes through a small aperture opposite the open- 
ing in the stage of the instrument. 
Unless the operating-room is in an elevated 
position, and the microscope, placed horizontally, 
looks out upon clear blue sky, it will be necessary 
to incline the instrument slightly, in the position 
of a telescope. It must be firmly fixed to its shelf 
in this position, and the elevation should be no 
greater than is absolutely required to effect the 
