160 
HisLOP^ on an Object-compressor. 
consists of a square block of mahogany^ about three inches 
by four_, across wbich a strip of brass is screwed, at a distance 
of one inch from one end, as a ledge, against which the glass 
slide is to be placed. A light trigger is jointed to the block 
in such a position that the end presses exactly in the centre 
of the slide. A steel or brass spring is fixed below the tail 
of the trigger, and beneath this a screw with a milled head 
is placed in such a manner as to increase the force of com- 
pression when it is unscrewed, by forcing the spring upwards, 
and vice versa. 
If preferred, a disc may be jointed to the trigger, so as to 
touch over an extended surface, or better still, a thin metal 
disc may be simply laid upon the cover, and the pressure be 
borne upon that. Care, however, must be taken that the 
balsam, or other cement, does not touch it, or inconvenience 
may result. 
The second form, fig. 2, is identical in principle, but is made 
Eig. 2. 
entirely of metal, and is useful when it is desired to apply heat 
at the same time as pressure, as it may be held over a lamp 
by grasping the prolonged end by the forceps, or it may even 
be fastened in a wooden handle. 
