viewed by Mkrofcopes . 45 
enquired after, and of the Grain of Sand, 
the fmall Seed, or whatever elfe is thought 
proper to compare with it, may be really 
meafured by a Ruler, or a Pair of Compaffes, 
and the Difference of their Diameters moil 
exactly found. 
The Method Mr. Hooke made ufe of, to 
know how much an Object appears mag¬ 
nified, I fhall give in his own Words.—- 
“ Having (fays he) rectified the Microfcope, 
ce to fee the defired Object through it very 
ce diftindly ; at the fame time that I look 
se upon the Objed through the Glafs with 
<e one Eye, X look upon other Objeds at 
te the fame Diflance with my other bare 
e{ Eye : by which means X am able, by the 
“ Help of a Ruler, divided into Inches and 
“ fmall Parts, and laid on the Pedeflal of 
fe the Microfcope, to caft, as it were, the 
“ magnified Appearance of the Objed upon 
ee the Ruler, and thereby exadly to mea- 
ss fure the Diameter it appears of through 
et the Glafs $ which being compared with 
the Diameter it appears of to the naked 
** Eye, will eafily afford the Quantity of its 
<c being magnified. 5 ’—This, for Multitudes 
of Objeds, is a ready and good Way ; and 
I can declare, from my own Experience, that 
a little Pradice will render it exceeding eafy 
and pleafant. 
Another very curious Way for this Pur- 
pofe is deferibed by the ingenious Dr. Jurin, 
in 
