MATHEMATICAL PAPERS. t57 
ter meafure. This was not done-at a fingle operation, but by 
a number of trials, till he found the bright part of the fun was 
in it’s leaft ftate. After reading off the numbers from the mi- 
crometer for the quantity of the eclipfe, Mr. Brown immedi- 
ately, at my requeft, took the length of the chord joining the 
culps, which I believe was done with great care, and found it 
1380. The micrometer meafures for the fun’s diameter was 
1906. Then 1906 — 1288 — 618, the eclipfed part, and 
v — — 3^ 53' digits for the greateft quantity of thc eclipfe, 
From the table which we made for the micrometer in the year 
1769, the fun's apparent diameter was 31/53”, exactly agree- 
ing with what Mayer's tables make it. I found the apparent 
diameter of the moon by the following method :—Let GFI 
be the fun, and HEB the moon, and EF the chord joining the 
fün's cufps. Now, as BG is a ftraüght line, bifecting the 
ftraight EF at right-angles, it muft therefore pafs through the 
centers both of the fun and moon. {Euclid 1. HI.) The 
angle ADE is a right-angle, and AE and ED are given quan- 
tities. a y AE — DE = AD. (Per Euclid 47. 1) 
AEE T tat 
Sum = 1643 3. 2156376 
_ Difference = 263 — 2,4199557. 
2)s. 6555933. 
xD spa 2. 8177966 
| AG— | 
Ties Lr $. DE eg 
GH= 1288 . x 
HD = 322,3 The 
