The A r £ a of GbjeBs . 49 
Object can be difMnguifhed through it. For 
which Reafon the greatsfi; Magnifiers never 
Should be employed but for the moil minute 
Objects.——This Consideration will direct 
how to fuit the Magnifiers to the Size of 
the Objedls to be examined, which is of the 
utmofl Confequence in Microfcopical Ob- 
fervations ; and may ferve to rectify the 
Miftake of Abundance of People unexperi¬ 
enced in Glaffes, who, upon, feeing a Mite 
or a Loufe greatly magnified, are apt to cry 
out with much Surprize, O that we had a 
Cricket, a Frog, or fome other Creature; 
how finely that would appear ! Whereas, in 
truth, Such large Objects would entirely cover 
the Lens, and could not be feen at all. 
Microfcopes very happily affifl us when 
Objects are fo fmall as to evade our Sight $ 
but it would be trifling and unneceffary to 
employ them on fuch large Things as we can 
fee without their Help, 
I fhall not trouble the Unfkilful with 
perplexing Calculations about the Area or 
Field of Objedts feen by each Magnifier ; 
but give this Short Rule in general, that it 
differs not greatly from the Size of the Lens 
made ufe of, and that the Whole of any Ob¬ 
ject, much beyond that Size, cannot conve¬ 
niently be viewed through it. 
There is fome Difference, as to the vifible 
Area of an Objedt, between Single and Double 
Microfcopes; for the Double Shew a larger 
E a Portion, 
