[ 7 ] 
of the Sector , which he made for them, hath now ren- 
dered it necdlefs, to enter upon any minute Dcfcription 
of mine at Wanjied ; both being conftruded upon the 
fame Principles, and differing in their component 
Parts, chiefly on account of the different Purpofes, 
for which they were intended. 
As mine was originally defigned to take only the 
‘Differences of the Zenith Diflances of Stars, in the 
various Scafons of the Year, without any View of 
difeovering their true Places; I had no Occafion to 
know exadly, what Point on the Limb correfponded 
to the true Zenith : and therefore no Provifion was 
made in my Sedor, for the changing of its Situation for 
that Purpofe. Neither was it necefiary that the Di- 
vifions or Points on the Arc fhould be fet off, with 
the utmoft Accuracy, Equidiflant from each other i 
becaufe, when I obferve any particular Star, the fame 
Spot or Point being firfl bifeded by the Plumb-line, 
and then the Screw of the Micrometer turn’d until 
the Star appears upon the middle of the Wire, that 
is fixed in the common Focus of the Glaffes of the 
Telefcope; I can thereby colled, how far the Star is 
from that given Point at the Time of Obfervation : 
and afterwards, by comparing together the fevcral 
Obfervations that are made of it, I am able to difeo- 
ver what apparent Change has happen’d. The Quan- 
tity of the vifible Alteration, in the Pofttion of the 
Stars, being exprelfed by Revolutions and Parts of 
a Revolution, of the Screw of the Micrometer; I 
endeavoured to determine, with great Care, the true 
Angle anfwcring thereto: and after various Trials, I 
thoroughly fatisfled myfelf, both of the Equality of 
the 
