iviii The Microfcope explained. 
Suppofe you have 25 revolutions, take out the num^ 
hers anl'wering to 10 and 5, add then) together, and 
you obtain your defire j or thus, 
Revol. 
20 - - 1466 
5 ~ " 733 
•- - -— inch, tenth 
Revol. - - 25 - - 2199 its Meafure ~z 2 — 1 -^ths. 
Example II. 
Suppofe we have 25 revolutions of the micrometer* 
ferew, they will be found equal to 2199, (as we have 
fhewn above), which is 2 inches i-ioths and 99-iGQ 
parts of another tenth, and if we apply the firft magnifier? 
which is fett in what is generally called a button, in the 
fecond table againft the firft number 1, will be found 
624 85, we reject the fractional parts, to prevent exag¬ 
geration, which fhews that number r, does at leaft in-? - 
creafe the image of the diameter of any object viewed 
through it 624 times. Therefore the object under con- 
fideration is 110 longer than 1-624th part of 2 inches 
i-ioth, and 99-100 parts of another tenth, which by 
the preceeding method of calculation will be equal to 
35-iPodredth parts of j-ioth of an inch. 
Example Ilf. 
If we had only two revolutions, which in the firft table 
anfwer to 293, this number exprefies as we have before 
fhewn, 2-ioths and 93-tooth parts of another tenth, 
tfie fame firft magnifier being applied to the microfcope.—?* 
The diameter of fuch an object would be no more than 
the 624th part of 2-ioths T 9 ^dredth parts of an¬ 
other tenth, which is equal to Tlfs^thoufandths parts 
of 
