T/oe Magnifying Power of Glajfes . 33 
From thefe Principles, it is eafy to find 
the Reafon why the firft or greatefl Mag¬ 
nifiers are fo extremely minute ; and alfo to 
calculate the magnifying Power of any con¬ 
vex Lens employed fingly in a Microfcope. 
For fuch as the Proportion of the natural 
Sight to the Focus of the Lens is, fuch will 
be its Power of magnifying. If the Focus 
of a convex Lens (for Example) be at one 
Inch, and the natural Sight at eight Inches, 
which is the common Standard, an Object 
may be feen through that Lens at one Inch 
diftant from the Eye ; and will appear, in 
its Diameter, eight Times larger than to the 
naked Eye. But as the Objed is magnified 
every Way equally, in Length as well as 
Breadth, we mull fquare this Diameter, to 
know really how much it appears enlarged ; 
and we fhall then find, that its Superficies 
is indeed magnified fixty-four Times. 
Again : Suppofe a convex Lens whofe 
Focus is at one Tenth of an Inch difiant 
from its Center : in eight Inches there are 
eighty fuch Tenths of an Inch ; and there¬ 
fore an Objed may be feen through this 
Lens eighty Times nearer than it can dif- 
tindly by the naked Eye. It will confe- 
quently appear eighty Times longer, and 
eighty Times broader, than it does to com¬ 
mon Sight; and as eighty multiplied by 
eighty makes fix thoufand and four hundred, 
fo many Times it really appears magnified. 
D 2 Tft 
