Graduation of AJlronomlcal Injlruments* 41 
be originally made with this view The piece of mahogany 
is to be affixed fo that one of its larger faces (hall be in a pa- 
rallel plane to the face of the platform, and fo low as to clear 
the under fide of the platform in its rotation ; and fo far diftant 
from the center, that an index may be fixed upon this upper 
face of the piece of wood, fo as conveniently to drop into the 
holes of the hoop ; while the common cutter frame of a clock- 
maker’s engine fhall be firmly attached upon the fame face of 
the wood, and fo fixed as to cut the edge of the dividing plate 
into teeth, anfwerable to the feveral divifions of the hoop. The 
teeth need only to be cut with a common cutter, making a pa- 
rallel notch : and here it will be proper to obferve, that not 
only both the index and cutter are to be founded on the fame 
piece or bafe of wood ; but that the nearer they are together, the 
more free they will be from the effefts of all variations of ex~ 
panfions by variations of temperature f, 
ST he equalifing the Teeth of the dividing Plate by grinding. 
The objedl of transferring the divifions of the hoop to the 
teeth of the dividing plate, is ftill farther to equalife the teeth 
by grinding ; efpecially thofe that, falling within the compafs of 
* After changing the pofition of the lathe, the collar of its mandrel fliould be 
removed, and the neck made to move within three planes, fo as to preferve an 
exact center, in the manner of an equal altitude inftrument. 
f It is proper to obferve, that as it may be impracticable to get the rim of the 
dividing plate call of the proper fize, in one entire piece, it will be very practi- 
cable, if cat of a lefs fize (fuppofe half), but of a fufficient thicknefs, to roll it 
down ; and by having the outward edge originally thicker than the inner, in the 
proportion of the radii, it may be fo managed by the rollers as to be of an equal 
thicknefs when brought to its proper fize. But the arms and center plate fhouid 
be of the fame metal, rolled in the fame degree. 
Vol. LXXVI. G 
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