Mr. Wollaston's Description 
turning separately on the axis of vision ; but, when once the 
two sets of wires are brought to be truly at right angles to 
each other, the cells can then be fixed together, and turned 
together, and finally settled in their place by screws and col- 
lars at the outside of the tube. These things, I believe, are 
new : I thought they might be improvements on the usual 
method ; yet I find the adjustment of the horizontal wires in 
collimation, might be dispensed with. 
My reason for having 3 horizontal wires, and at about that 
distance, was, that after having ascertained what the dif- 
ference is, I might observe the lower limb of the sun or moon 
at the one, and the upper limb at the other of the extreme 
wires, without much altering the elevation of the telescope, and 
removing the centre of the object, or preceding and subsequent 
limbs of the sun or moon, far out of the centre of the field. 
The divisions on the circle itself come now to be spoken to. 
They were done by hand ; and have been executed with 
great care. The original divisions are by dots or points, at 
every ten minutes. Within, is another row, by strokes or cuts ; 
laid off from the points to every ten minutes likewise. The 
dots are what we will regard first : the cuts afterwards. 
As it always appears to me convenient, in actual observa- 
tion, to contrive that every thing shall do itself, as far as I 
can, and to leave the mind as well as the body at perfect 
ease, and totally disengaged from calculation ; I considered, 
that making both the microscopes talk the same language, 
read off the same way, with the guiding figure always to the 
same hand, and the dot to be observed to the same hand too, 
and the readings always positive, would conduce much to 
