for Opake Gbjedfs . 
when fuch come under Examination, it will 
not always be proper to throw on them the 
Light reflected from the Speculum : for the 
Light tranfmitted through them meeting the 
reflected Light, may, together, produce too 
great a Glare. A little Practice will teach 
how to regulate both thefe Lights to good 
Advantage. 
There is Reafon to expedt great Difcove- 
ries may be made by the Apparatus above 
defcribed, as opake Objedts are a large Field, 
but little hitherto examined, by reafon of 
the great Difficulty in doing it. 
Having given a Defcription of the feveral 
Sorts of Microfcopes in Ufe amongft us at 
prefent, and ffiewn what particular Advan¬ 
tages may be expedted from each, I ffiall 
proceed to inifrudl; the Ignorant in thefe 
Things, with ail the Clearnefs I can, to find 
out the magnifying Powers of the Glades 
they make ufe of, and calculate how many 
Times they enlarge the Diameter, the Super¬ 
ficies, and the Cube ^ or folid Square of any 
Objedt under Examination. And this, I 
perfuade myfielf, will be highly fatisfadtory. 
Some, pernapsj may djflike my fuppo ing the Cube of 
an Object to be magnified, fince, in reality, the Superficies 
only can be feen : but the Neceffity of fuch aSuppofmon will 
appear plainly in the Progrefs of this Work, when we come 
to confider the true Size of Microfcopical Gbje&s, by com. 
paring them with larger Bodies. 
Vol. I. D 
and 
