VOL. LII.] I'HILOSOPHICAL TRANSACTIONS. 655 



servation, is not required; all that is necessary to be known, is the time of du- 

 ration from the internal contact at the ingress, to the internal contact at the 

 egress, and that the clock moved equably during the interval of the contacts, 

 and that the least distance of the centres of the sun and Venus, as seen from th^ 

 centre of the earth, is also known. 



The method I have followed in this inquiry, was by finding the total duration 

 at the centre of the earth : in order to find this, it was necessary to know the 

 least distance of the centres of the sun and Venus as seen from the earth's centre. 

 By the measurements of the distance of the limb of Venus from the sun's limb 

 taken at Savile-house, and also by the like measurements taken by Mr. Haydon 

 at Leskeard, I found, on the above supposition of the sun's parallax, that the 

 least distance of the centres, as seen from the centre of the earth, was = 9' 31". 

 The total duration therefore at the centre of the earth was 5^ 58"^ V. I have 

 compared the several observations of the total duration with this central duration, 

 and from each I have determined the sun's parallax, as may be seen more fully 

 „, in the following table. I have inserted in this table the alteration of duration by 

 one second of the sun's parallax at each place, by which may be seen the quan- 

 tity of error in the determination of the sun's parallax arising from any quantity 

 of error in the observation. 



The times of the total duration at those different places I have taken from the 

 Phil. Trans. ; only those of Calmar and Cajaneburg I have taken from the 

 Swedish acts; the internal contact at the ingress at Cajaneburg, in those acts, 

 is at 4^ 18"^ 5% whereas it should be at 4*^ 19™ 5^, as may be easily proved, this 

 being an error in writing down the minutes, which has happened more than once 

 in these observations, occasioned by the hurry of writing down the times 

 of the observations. The observations in the East Indies I have taken from 

 letters sent by the East India Company to the r. s. I have also been obliged to 

 make a correction of the minutes in the observation at Tranquebar and at the 

 Grand Mount, a place about 8 miles to the s.w. of Madras. 



