MATHEMATICAL PAPERS. 131 
of about an inch focus... We determined the magnifying power 
of our telefcopes by Hawh/bee’ s method. 
- We fat down to our: telefeopes about ten minutes Bore 
eleven o'clock, in a garden adjoining the room where the clock 
was fixed, and were fo fituated, that we could all very diftin@ly 
hear the perfon who counted the clock. Before we began to 
obferve, we agreed that each one fhould note his times of ob- 
fervation, without fpeaking to the others, that all might deter- 
mine for themfelves, and no one might be in danger of being 
difcencerted. 
We had a favourable time for obferving the beginning and end 
of the eclipfe. The immerfions and emerfions of a number 
of the folar fpots were attended to by us ; the fituations of 
which, upon the difc, we determined as near as we could, a 
little while before we fat down to our telefcopes. They then 
appeared to us as in Plate IT. Fig. II. Mr. Prince had fixed 
parallel hairs in his refractor, dividing the fun’s difc into four 
equal parts, horizontally. Thefe hairs, together with a verti- 
cal one in the center, affifted us much in diee the Jen of 
the fpots. 
-As we had no micrometer to meafare the rasa ta ^ the 
eclipfe, we determined it by Dr. Wallis s method, publifhed in 
Whifton’s Aftronomical Lectures, p. 188, 189. The eclipfed 
parts of the fun, marked at the time of the greateft obfcura- 
tion, we afterwards meafured upon a diagonal fcale drawn for 
the purpofe, by which we could determine to the &fticth part 
of a digit. 
At the middle of the eclipie, id for fome time before and 
after it, there was a very great chilnefs in the air, and fo much 
_ dew ate that the papers we ufed abroad became quite damp. 
R 2 The 
