i Mr. Smea?on*s Obfervatms on the 
and Hevelius laboured this part of their inftruments with 
their own hands ; and though public rewards have at length 
brought forth different methods of dividing from our befl 
artifts, which have been communicated to the Public ; yet I 
truft it will be thought, that if any thing relative to this 
bufinefs remains yet behind, that may tend to furnifh the 
ingenious artifts, who are cultivating this field, with any new 
or curious idea upon the fubjedt, it will be well worth communi- 
cating to this learned Society : fince, if an hint, which is 
effentially different from any thing that (fo far as I know) the 
Public is in poffeffion of, be once ftarted, and is purfued and 
worked upon by ingenious men, it is not pofiible to fay, to 
what valuable purpofes it may be converted. 
This, perhaps, will better appear by taking a fliort review 
of the labours of others, from the time of Tycho Brahe 
and Hevelius (who did not ufe telefcopic fights) to theprefent 
time. 
The very learned, ingenious, and inventive Dr. Hook, in 
his Animadverfions on the Machina Cceleftis of Hevelius* 
publifhed in the year 1674, has given us an elaborate defcrip- 
tion of a quadrant, whofe divifions were formed, and after- 
wards read off, by means of an endlefs fcrew, working upon 
the outermoft border of the limb of a quadrant; which, he 
fays, does not at all depend upon the care and diligence of the in - 
Jlrument -maker in dividing , graving , or numbering the divifions , 
for the fame fcrew makes it from end to end ; yet he has given us 
no account of any particular care or caution that he ufed, in 
preventing the fame fcrew from making larger or fmaller paces, 
in confequence of unequal refiftance, from a different hardnefs 
of the metal in different parts of the limb ; nor any method of 
sorredting or checking the fame ; nor of making a fcrew, the 
4 angle 
