4 Mr. Smeaton’& Defcription of an 
the feet fin die PQ, which is firmly focketed into it at K, 
according to the dotted lines o r, o r. The axis of this fpindle is 
therefore capable of being fet upright upon the zenith point , 
and to maintain that pofition with a fufncient degree of fitm- 
nefs. — Ry, Ry, reprefents the fecfion of a brafs focket made to 
fit the fpindle, and turn round freely upon it ; and when home 
to the (houlder at 00, to turn without fhake ; the focket and 
fpindle being a fmall matter taper, and ground together. On 
one fide of the focket is firmly fixed the arm ST, by {crews or 
folder. — UVV is an arch of So degrees, ferving inftead of the 
quadrant of altitude, and of the fame fob fiance as the meri- 
dian. This is firmly fcrewed to the arm, and adjufted by 
conftruCtion, fo that when the fpindle is vertical, the face of 
this arch fhall make part of a vertical circle. — This arch being 
a portion of a circle, of the fame diameter as the brafs meri- 
dian, when its point zero at W refts upon the brafs horizon, 
its infide furface is made to agree with that of the horizon 
by means of a fmali thin nib of brafs ; that being attached to 
the infide of the bottom of the quadrant of altitude at W, and 
projecting a little below it, gently bears againft the infide 
of the horizon, in fubftance occupying about half the clearance 
between the body of the globe and its furrounding horizon ; 
this nib 9 feen edgeways, is fhewn at the letter X. By this 
means the altitude of the objeCt is fhewn upon the working face 
of the quadrant, and the quadrant’s bottom fhews the azi- 
muth upon theTorizon ; at the fame time the globe is free to 
revolve upon its axis, clear of all the circles* 
The quadrant might be made complete to 90° ; but as in 
thele middle latitudes there is very little bufmefs for azimuths 
when the altitudes are above 8o°, and as I judged it eligible, 
that the quadrant fhould be made capable of working on both 
lides the meridian ; that would be prevented by the n e cellar y 
2. thicknefs 
