320 Mr. Smeaton’s Obfervation of Mercury 
fame time more effectually to anfwer the purpofe of Graham’s 
agronomical fettor, which was contrived by him (as Dr. 
Smith informs us) to fupply the deficiencies of the micrometer 
then in ufe *. 
The mod neceffary and fundamental improvements feemed 
to be ; fir ft, that of rendering the micrometer telefcope ma- 
nageable upon an equatorial motion ; and, feconaly, the con- 
trivance of a ftand of fuch folidity and ftedfaftnefs that the 
telefcope might preferve the pofition in which it was placed, for 
a length of time : for it occurred to me, that if the telefcope 
could be maintained at reft ; or in a degree of {lability fupe- 
ricr to that of the agronomical feflor ; then the neceffity of 
taking in a greater ccmpafs in declination than could be com- 
modioufly given to the field of a telefcope would be the lefs 
neceffary : for, inftead of confining the object to a comparifon 
with a flar not differing more than a few minutes of time, or 
at moft a quarter of an hour in right afcenfion, thofe com pa- 
ri fons could be extended to an hour or two, or even on occafion 
to three or four hours; there being fcarcely any part of the 
heavens fo devoid of ffars, of a fuitable magnitude for thefe 
obfervations, but that a proper one may be found within 
that compafs in right afcenfion, provided there is allowed 
micrometer were from ten to fifteen feet long, made with wooden tubes, flip- 
ported at each end upon two wooden fupports, by which the telefcope could be 
managed in al itude and azimuth j but not to follow a celeRial object in its proper 
motion on one center:, which apparatus, I believe, is Rill remaining in the 
Royal Obfervatory. 
* This inflrument is defcribed in Smith’s Opt i«rs, Vol. II. p. 35Q. ; and the 
original one, made by Mr. Graham, was, at his death, placed in the Royal 
Obfervatory, and is mounted upon a three-legged Hand of wood. 
I 
the 
