142 PHILOSOPHICAL TRANSACTIONS. [aNNO 172.6. 



seems accompanied with circumstances that argue its exactness, was likewise 

 very well observed at Wansted in a 15-foot tube, at ^^ 28™ IT apparent time, 

 the difference being 37"" 12'. 



These are the only observations among those whicli were last communicated, 

 that Mr, P. could compare with any degree of certainty with his own. But 

 others were printed in the Phil. Trans. N° 385, which were likewise made by 

 the same curious persons, who observed an emersion of the first satellite at 

 Lisbon, Sept. 2, 1724, N. S. at ^ 36" 57". This was seen also at Wansted 

 in the reflector at 10*' 13"' 28^ apparent time. Hence, allowing for the differ- 

 ent telescopes, the difference of meridians is 36™ 45\ 



This emersion at Wansted preceded the calculation by the tables 4™ 40^ : 

 and another emersion observed with the same telescope on Sept. 18, N. S. pre- 

 ceded the calculation 5™ 10^ We may therefore suppose that on Sept. 9, N. S. 

 the true emersion at Wansted preceded the computed about 4™ 52*. The 

 emersion that day by the tables was at 12*' 15'" 34^ app. time; therefore the 

 true emersion at Wansted was at 12*^ 10"' 42\ At Lisbon it was observed at 

 ll^ 34" 26^ So that, allowing for the difference of telescopes, the difference 

 of meridians by this observation is 36" 30^ * 



The mean of all these differences is about 36" 58', from which subtracting 

 28' for the difference of meridians between London and Wansted, the remainder 

 will be the difference of meridians between London and Lisbon, vi?. 36-i-" = ^ 

 7l', Lisbon being so much to the westward of London ; which is about 5-i.' 

 greater than what is determined in the forementioned Transaction. 



The same Transaction containing some observations of eclipses of the same 

 satellite made in the Fort of New York, communicated by his Excellency 

 William Burnet, Esq. governor of New York. Mr. Pound takes this oppor- 

 tunity of determining the longitude of that fort more exactly than it can be 

 supposed to be there done, by the bare comparison of the observations with 

 the tables ; having two observations made at Wansted, which tally with two 

 made at New York, on Aug. 25, and Sept. 10. 



By the observation made Aug. 25, 1723, O. S. which is esteemed the most 

 distinct and best, the satellite emerged at 9^ 35" 14^ by the clock, which went 

 about 1J-" too fast for the apparent time at the emersion, as appears by the alti- 

 tudes of the sun's limb taken the morning before and after the observation; so 

 that the emersion at New York was at g'' 34" apparent time, that is, 9'' 32" 20^ 

 mean time. 



Aug. 27, S*' 57" 40' mean time, the satellite was seen emerging at Wansted 

 in the reflector; and Sept. 12, 7'' 17" IS"* mean time, it was seen emerging 



