"22 ftfr. Smeaton’s Obfervatlons on the 
one ; ' furthermore, that the fcrew and wheel, being ground 
together as an optic glafs to its tool, produced that degree of 
imoothneis in its motion that I obferved ; and, laftly, that 
fhe wheel was cut from the dividing plate : yet, how the 
dividing plate was produced, he for particular reafons referved 
to himfelf. 
Nor can he be blamed For the refervation of this one fecret ; 
as he had, even at the time of my early acquaintance with 
him, a kind of forefight that from the fuperior merit of Had- 
ley’s quadrant, a demand for that, and other inftruments for 
the purpofe of navigation, was likely to increafe ; and that he 
might live to fee a public reward offered for a method of di- 
viding them with greater accuracy and difpatch than had at 
that time appeared. Indeed, he had himfelf an idea, from the 
fatisfaflory fuccefs that had attended his operations in dividing, 
that a fcrew and wheel, produced from his engines of one 
foot diameter, would have as much truth as the eight- feet qua- 
drant at Greenwich : and though he doubtlefs greatly over- 
rated the accuracy of thefe miniature performances, yet it does 
not follow, as his methods were not confined to fo narrow a 
compafs, but that, his fcale of operation being proportionally 
enlarged, a degree of accuracy in the graduation of aftrono- 
mical inftruments may be attained in proportion. 
X muft here beg leave to obferve, that there appears to me to 
be a natural limitation to the accuracy of inftruments, con- 
fiding of confiderable portions of a circle, fuch as quadrants, 
&c. I do not find that the fineft ftroke upon the limb of a 
quadrant, made by Bird’s own hand, if removed from its 
% The zenith fe£tor confifts but of few degrees, with little variation of its 
jpofition inufingit, 
i coincidence 
