138 Mr . Wollaston's Description 
springs, included in a tube, are applied through rings within 
the connecting plate above mentioned. These carry, each of 
them, a pair of rollers, on which a brass collar at each end of 
the axis of the telescope rides. The springs may be used or 
removed, at pleasure ; and they can be strengthened or 
weakened, by means of a screw at the bottom of the tube, so 
as to take off from the pivots any part of the weight that ma}’ - 
be judged best : and, since they are in a line with the axis, 
and are made capable of obeying it in every direction, there 
is no danger of their deranging its adjustments, while they 
render its motion exceedingly light and smooth indeed. 
The adjustments of the Y s are both of them at the same 
end of the axis, opposite to the divided circle and the micro- 
scopes ; because the smallest adjustment of that end of the 
axis between the microscopes, would have affected them so as 
to require an entire re-adjustment of them too. At the farther 
end, the axis is perforated, to admit light for illuminating 
the wires. And I find that (to my sight at least) it is much 
most agreeable to close the aperture with a pale green glass. 
The axis itself is 18 inches long, exclusive of the pivots, 
which are about each. 
The microscopes need no description. They are on the 
same principle as those described by our late member Major 
General Roy. (Phil. Trans. Vol. LXXX, p. 145 ) Mine are 
9 inches long ; the object-end at 2 inches from the limb of 
the circle. They magnify 24 times. One revolution of the 
micrometer-screw is equal to one minute ; and the head is 
divided to seconds. 
The fixed or stationary wire in them, is at the first notch, 
or minute itself ; and it is adjusted by means of a plumb-line. 
