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Mr . Smeaton’s Defcription of an 
them for the laft mentioned purpofe, will find them more 
defective in fome refoedls than thev are in others. 
i- •/ 
The difficulty that has occurred in fixing a femicircle, fo 
as to have a center in the zenith and nadir points of the globe, 
at. the fame time that the meridian is left at liberty to raife the 
pole to its defired elevation, I fuppofe, has induced the globe- 
makers to be contented with the frip of thin flexible brafs, 
called the quadrant of altitude ; and it is well known how 
imperfectly it performs its office. 
The improvement i have attempted, is in the application of 
a quadrant of altitude , of a more folid conftrudtion ; which 
being affixed to a brafs focket of fome length, and this ground* 
and made to turn upon an upright fteel fpindle, fixed in the 
zenith, fteadily directs the quadrant , or rather arc , of altitude 
to its true azimuth , without being at liberty to deviate from a 
vertical circle to the right hand or left : by which means the 
azimuth and altitude are given with the fame exaCtnefs as th 6 
meafure of any other of the great circles. 
With refpeft to the horary circle, as the common application 
feems very convenient on account of the ready adjuftment of 
its index to anfwer the culmination of any of the heavenly 
bodies ; and as I find that a circle of four inches diameter is 
capable of an aftual and very diflinguifhable divifion into 720 
parts, anfwerable to two minutes of time each, which may ferve 
a globe of the largeft fize ; it feems that it fhould rather be im- 
proved than omitted ; and, if inftead of a pointer , an index flroke 
is ufed in the fame plane with that of the divifions, the fingle 
minutes, and even half minutes, may be readily diftinguiffied. 
This globe, though mounted merely as a model for experi- 
ment, and only nine inches in diameter, appears capable of 
bringing out the foiution to a quarter of a degree ; which, I 
appre- 
