great magnifying Powers ufed by Mr, Herfchcl. 175 
by one plain analogy : viz, as the image of the wire by the firfl 
lens (77 1) is to the power it gives to the telefcope (163. 8), fo 
is the image of the wire by the fecond lens (1 19) to the power 
it will give to the fame telefcope (250.7). The particulars of 
all the meafures are as follows : 
Powers as 
they have 
been called 
in my papers. 
mages of a wire throwr 
upon a paper in hundredths 
of half inches. 
A mean of 
the four 
meafures. 
Powers as they 
come out by this 
method. 
146 
CO 
78 
78 
77 + 
163.86 
_ 1 * * * 7 ° 4 
1. 04 
227 
I 19 1 19 
11 9 
1 19 
I 19 
2 5°-7 
278 
'43 1 43 
144 
i 43 
J 4 3 i 
301.8 
r 
236 236 
2 3 5 
236 
2 35 *] 
460 - 
Smaller wire.. 
496.7 
53 54 
55 
54 
54 J 
754 
s 3 8 5 
84 
85 
8 4 j 
775 * 1 
93 z 
10 7 107 
107 
108 
107I 
986.7 
11 59 
128 128 
129 
128 
1 28^ 
1 1 79.9 
1 53 6 * 
An excellent lens, loft about eight months 
ago. 
2010 
■236 236 
238 
3 3 6 
2 3 6i 
2175.8 
3 1 68 
2§I 283 
281 
280 
281 \ 
2 S S S-S 
6450 
6 35 6^5 
630 
626 
6 2 9 
5786.8 
I beg leave, Sir, now to give a fhort defeription of the method: 
I have formerly ufed to determine thefe powers. In the year 
1776 1 ere&ed a mark of white paper, exactly half an inch in . 
diameter, which I viewed with my telefcope at the greateft 
convenient diftance with one of the leaf: magnifiers. Am 
afftft ant was placed at redf angles in a field, at the fame diftance 
from 
