liv The Microfcope explained. 
The above analogy will anfwer to every compound 
microfcope, but the refult will not be the fame. 
The next enquiry is the minutenefs of the object itfelf, 
which requires a table fhewing the apparent fize of ob- 
jedts feen under the various revolutions and parts of a 
revolution of the micrometer fcrew; to perform this. 
Put on any magnifier, as No. 4, and the fectoral 
glafs-fcale on the ftage, raife or deprefs the microfcope 
till the objecft appears diftindf, meafure the diftance from 
the ftage, to the hole, thro’ which the needle enters the 
body of the microfcope, then apply the micrometer, and ad- 
juft the point of the needle to the edge of the field of view, 
count how many whole revolutions the micrometer- 
fcrew makes in palling acrofs the diameter, which we 
find to be 40, now multiply 40 by 20, (the number of 
parts the dial-plate is divided into), and we {hall obtain 
its meafure to be equal to 800 thoufandth parts of an 
inch, its double is equal to 1600. 
The meafure of the diftance from the ftage to the 
needle-point, as found above, being equal to 640, to 
which adding the double focus of the eye-glafs rzc 240, 
we obtain 880 parts for the diftance of the eye from the 
object, then doubling the number found on the micro¬ 
meter, which is ] 600 ; fay, 
As the diftance of the eye from the image 240: is to 
double the meafure of the feild of view 1600 :: fo is the 
mean diftance of the eye from the object 880: to a fourth 
number 586,666, whiph divided by 40, the No. of revo¬ 
lutions of the micrometer-fcrew, produces 146.666 thorn? 
fandths parts of an inch. The two tables follow : 
Table I, 
