Graduation of Afr Gnomical Inf rum mis, - 3 r 
be wrought to a right line in contiguity to each other ; by thu 
means the ftraight edge of each of the ft raps will be reduced 
to the fame diftance from the fteel hole : the hard fteel edges 
maybe redlified by the grindftone, if neceffary. 
This being done, not only the holes in the chaps, but the 
holes in the two fteel plates, applied to each other, like the 
two fides of the chaps, muft be refpedlively ground together ; 
not with a taper pin, as prefcribed by Hindley ; but fo as not 
only to be cylindrical, but that the fame cylindrical pin fhall 
equally fit them all, and leave them fmooth and poliffied ; 
which is a procefs no ways difficult to a curious artift, and of 
'which therefore a minute defcription is unnecefiary. 
The chaps being then put upon one of the {traps, with its 
ftraight edge uppermoft, and a pin put through the holes on 
the left-hand, and through the fteel hole in the ftrap under 
operation, the chaps muft be let upright, fo that the line join- 
ing the centers of the holes {hall be parallel to the upper edge 
of the ftrap; thebrafs plate, mentioned by Hindley, between 
the chaps, as a guide for directing them always to that upright 
pofition, may be then adjufted and fixed to the infide of the 
chap next the operator 
.The performance of the enfuing part of this work (hould be 
at a feafon when the temper of the air is not very variable ; 
rather above the mean temper (fuppofe at 6o°) than below it ; 
* It would be wfell, previous to the drilling of the fleet chaps, that another 
hole was drilled in the chaps, that {hould be fomewhat above the upper edge of 
the ftraps, and in the middle betwixt (ide and fide, to receive a jleadyfln therein, 
antecedent to drilling the main holes ; for then a tempered fteel pin, a little taper, 
will, by driving it in as far as neceflary, conftantly anfvver this purpofe from firft 
to laft, fo as to regulate the holes in grinding, to be truly oppofite : proper holes 
•ihould aifo be drilled for fixing the' brafs guide plate to one of the chaps, 
Vol, LXXVL F -but 
