VOL, 



LIII.] 



PHILOSOPHICAL TRANSACTIONS. 



*9 



Bencoolen, where it was first proposed to send Messrs. Mason and Dixon, the 

 difference would have been about 44. minutes. At the island of Rodrigues, 

 where Mr. Pingre could only observe the last internal contact, the difference 

 would have been about 7-^ minutes. On the southern coast of New Holland, 

 it would have been somewhat more than 10 minutes. And in the great Indian 

 Ocean, under 115-5- of absolute longitude from the Isle of Ferro, and in 37° 

 of south latitude, where the beginning of the transit would happen soon after 

 sun-rising, and the end just before sun- set, the difference would amount to 134- 

 minutes. The greatest difference between the interval of the two internal 

 contacts, as determined by actual observation on the 6th of June, was 

 2"* 49'.75, a quantity hardly sufficient to determine the sun's parallax agreeably 

 to the method proposed by Dr. Halley. 



Mr. H. has however made the necessary calculations, and compared the 

 duration of the transit observed at several places with the duration as observed at 

 Tobolski. The parallax resulting from each observation is contained in the fol- 

 lowing table, in which the 3d column contains the observed duration, the 4th 

 the difference of each observed duration ; the next contains that difference as 

 deduced by computation on a supposition that the sun's parallax is 9*. In the 

 last column is given the horizontal parallax on the day of the transit, resulting 

 from a comparison of the 4th and 5th columns. 



Mean of the whole 



Mean, rejecting 2 observations at Upsal and 1 at Tornea. 



9332 

 9.579 



• The duration at Cajaneburg was the shortest, except at Tobolski ; with 

 which if we compare the duration observed at Madras, the parallax is 9''''.948 : 

 and by taking a mean of the parallax deduced from a comparison of the obser- 

 vation at Madras with those of Tobolski and Cajaneburg, the parallax is 

 9''.76'2. The observations at the above places agree as well together as can be 



VOL. XII.' H 



