Graduation of Agronomical Infrurnents . 17 
equally unexceptionable with the 96 arc ; and confequently if, 
inftead of the 96 arc, another arc of 90 was laid down (which 
being upon a different radius, its divifions will ftand totally un- 
connected with the former), then thefe two arcs would in reality 
be a check upon each other; for being of equal validity, the mean 
might be taken : and if (in lieu of vernier divifions) ftrokes at 
the diftance of any odd number, as 7, 9, 11, or 13, are marked 
upon, and carried along with, the index plate ; thefe will pro- 
duce a check upon neighbouring divifions ; and the angle may 
then be deduced from the medium of no lefs than four 
readings. 
The laft works that have been made known to the public in 
the line of graduation (fo far as has come to my knowledge) are 
thofe of the very ingenious Mr. Kamsden, which were pub- 
lifhed, by order of the Board of Longitude, in the year 1777. 
From his own information, I learn, that in the year 1760 
he turned his thoughts towards making an engine for dividing 
mathematical inftruments ; and this he did in confequence of a 
reward offered by the Board of Longitude to Mr. Bird, for 
publifhing his method of graduating quadrants ; for as, feveral 
years previous to that period, he had taken great pains to ac- 
compliih himfelf in the art of hand-dividing, in which line 
Mr. Bird had acquired his eminence, he conceived by this pub- 
lication of Mr. Bird’s he fhould be reduced to the fame ftandard 
of performance with the reft of the trade* He, therefore, partly 
to fave time, and that kind of wearinefs to an ingenious mind 
that ever muft attend the endlefs repetition of the fame thing 
from morning to night; partly ftill to pteferve the pre-eminence 
he had then gained ; and partly to procure difpatch in the great 
increafeof demand for Hadley’s fextants and oCfants, in confe- 
quence of the fuccefsful application of the moon’s motion to the 
Vol. LXXVL D purpofe 
