158 REDFERN, ON AQUARIA. 
adapted to tighten it by a contrivance similar to that in the 
case of the rmg, c. A piece of the rim of the cap was cut 
out to the extent of five-eighths of an inch at /, and a thinner 
piece of brass, soldered only at one edge, was substituted for 
it. A ring of thin brass, n, having a projecting piece, 9, 
fixed to it by hard solder, was then applied and soldered 
around the rim, with its projection, 0, over the space, /, from 
which the edge of the cap had been removed. The screw, 
k, working through 0, presses the thin plate of brass, m, upon 
the edge of the brass disc, and without injuring the smooth- 
ness of its surface, tightens the joint to any required extent. 
p is a lever or arm of one-inch brass tube, twenty inches 
long, sliding through the tube, A, and rotating within it. One 
end of this lever is left open to receive a cylindrical piece of 
lead, which is sometimes useful to balance the lever when 
used with its arms of very unequal length; the other end is 
closed by the cup of a large ball-and-socket joint soldered 
into it. Loosening of this joint is prevented by the pinching 
screw, 7”. To the ball is attached a short arm, carrying the 
piece of tube, s, three inches long, sawn through lengthwise 
at the part most distant from the ball, and cut away as re- 
presented on the figure, so as to hold the tube of the body 
of the microscope loosely enough to allow of easy sliding and 
rotation for focal adjustment. I have the stem attached to 
ball made of two pieces screwed together, so that I can sub- 
stitute a cell holding a single lens or a doublet, to be used as 
a simple microscope, for the split-tube carrying the body of 
the compound instrument. To diminish the weight of the 
body of the compound microscope, I make it of paper pasted 
to form a thick tube, which is lined with black velvet. An 
adapter, carrying the lenses, slides into it tightly at one end 
and the eye-piece into the other. 
When in use, the most favorable position for the transverse 
arm, p, is near that represented in the woodcut, where it 
forms a lever with arms of unequal length. After coarse 
adjustment, by sliding the body of the microscope through 
the split tube, s, a very convenient fine adjustment is made by 
acting on the long arm of the lever. 
It will easily be understood that a considerable range of 
movement of the body of the microscope is allowed by the 
ball-and-socket jomt—by the movements forwards and back- 
wards, and of elevation and depression of the arm or lever, 
p, without shifting the place of the foot, a; whilst by chang- 
ing the position of the foot, and that of the ring, c, on the 
vertical stem, the whole of a surface not higher than two 
feet may be examined with readiness. When the transverse 
