MATHEMATICAL PAPERS. 25 



^yas fixed, that I was not so far satisfied with them at the time, 

 as to suppose they could be safely used to determine the 

 least distance of centres : but was persuaded, that if the ob- 



servations of the 



1 Ije as fivourable 



those of the two first, the least distance of centres, and the 

 latitude of Mercury, might with more accuracy, be deduced 

 from the contacts, than from any of the micrometer mea- 

 sures. I did not attempt, on the same account, to measure 

 Mercury's scmidiametcr by the micrometer, but left it to be 

 determined from the contacts. As the Sun's diameter was 

 a large angle, and. could more easily be taken than small 

 ones, I applied the micrometer several times, to measure it, 

 when the wind Avas least troublesome; and found it, parallel 



with the horizon, to be 32' 2r 33. 



The atmosphere was perfectly clear at the time of the two 

 last contacts; and I found the internal one happened at 

 P 15' 44". p. M. and the external one at 1*^ 17; 36" P. M. both 

 ajiparcnt time. 



I took corresponding altitudes of the Sun on the day of the 

 transit; and found, that when it passed the meridian, it was. 

 by my clock, using the proper equation for change of decli- 

 nation, IP 59' 36" 22'". From the 2d of November there- 

 fore, to the 5th, the clock had gained upon apparent time 

 3" 5'". If it had kept mean time exactly, it would have 

 gained 3" 54'". Hence it appears, that it deviated but about 

 J of a second in twenty four hours, from keeping mean 

 time. 



Having had so good observ^ations of this phenomenon, I 

 thought it my d-uty to communicate them to the Academy. 



D ' And 



