170 
MR. LLOYD ON THE DIFFERENCE OF LEVEL BETWEEN 
The legs, which are very strong, are iron-shod, and braced at the bottom, about 
six inches from the shoeing, with three thick iron rods, rendering the whole 
steady, and affording the men a purchase to press down with their feet, and 
rough level the stand ready for the reception of the instrument. 
Adjustments. 
The above instrument requires several adjustments, which I shall endeavour 
to describe in the order they are made. 
First, To make the low r er level parallel to the axis of the telescope : 
Place the telescope directly over one of the foot-screws, and clamp it ; then 
bring the bubble of the level, by means of the foot-screw, to the same division 
on either side the graduated scale affixed to and over the level, taking care 
that the bubble of the little level at the eye end of the tube (and at right 
angles to the large level) is in the centre ; then reverse the telescope in its 
collars, observing if the bubble reaches to the same division, and correct one 
half of that number by the pushing screws on the level itself, and the other 
half by the foot-screw : this must be repeated until the bubble remains in the 
same spot. 
Second, To place the large level in the same vertical as the axis of the 
telescope : 
Move the telescope in its collars until the level is brought considerably to 
one side, and observe if the bubble still remains at the same division ; if not, 
move the side pushing screws on the level, until the bubble has returned to its 
proper place ; move the telescope again as much to the other side, and observe 
if the bubble comes to the same division ; if not, it must be re-adjusted, until 
it is as near as the accuracy of the grinding of the level will allow. 
These two adjustments are naturally dependent on one another, therefore 
they must be both examined, until no alteration in the bubble can be per- 
ceived. 
Note . — As the collars may wear a little hollow in time, care must be taken 
that one particular shoulder of the two collars rests against the Y when reversed, 
in order to use the same point of support. 
Third, To place the axis of the telescope parallel to the plane of the instru- 
ment : 
