c £he Magnifying Tower of Glajfes. 39 
ting the Screen at further Diftances, you 
may magnify your ObjeCt to almoft what 
Size you pleafe. But I would advife all 
who ule this Sort of Mierofcope, to regard 
Diftinttnefs more than Bignefs, and place 
the Screen juft at that Diftance where the 
Object is feen moil fharp and clear. 
CHAP. IX. 
Of the Magnifying Power of Glajfes in the 
Double Mierofcope. 
I Should now ihew the Method of com¬ 
puting the magnifying Power of our 
Double Mierofcope, as I have done of the 
Single ones: but a Calculation of the Powers 
of three combined Glaftes would appear fo 
intricate and unintelligible to People unac¬ 
quainted with Optics (for whole Service 
chiefly I intend this Treatife) that I believe 
they will readily excufe my perplexing them 
with it: and as for the Learned in that Sci¬ 
ence, they probably will be better pleafed 
to calculate for themfelves. 
The Double reflecting Mierofcope, deferi- 
bed p. 16. is the only Inftrument at prefent 
made amongft us for this Purpofe, wherein 
fuch a Combination of Glaftes is employed. 
Here, indeed, the magnifying Power of the 
ObjeCD 
