VOL. LIX.] PHILOSOPHICAL TRANSACTIONS. 675 



by a black protuberance or ligament, which was not broken by the entrance of 

 the thread of light, till 4 seconds after the regular circumference of Venus seemed 

 to coincide with the sun's. 



The telescope Mr. Biddle made use of for viewing the transit, was a reflecting 

 one, belonging to the Philadelphia Library Company, the speculums of which 

 are 2-h- feet apart, and the lenses in the eye tube 4 inches apart ; it was the least 

 magnifying power that he used, as he found the tremulous motion too much 

 magnified by the other power. The small one was in good order, and defined 

 the sun's limb, and spots on its disk, very clearly. He had applied a polar axis 

 to it, and made some rack-work, by which he could keep the same part of the 

 sun's limb in the field with ease ; his companion was not so well provided with a 

 telescope, the one he used being of DoUond's refracting glasses of 44- feet. This 

 they fixed, with a ball and socket to a post, by which it was easily directed to the 

 sun. Thus furnished, they found the contacts to take place as follows, reduced 

 to mean time. 



Owen Biddle's external contact at 2^ ] 1™ 53' 



internal one at 2 29 53 



Joel Bayley's external contact was lost by an accident, but seen by 



him, after it had taken place, at 2 12 15 



internal ditto 2 2Q 53 



The internal contact, given by Owen Biddle, is at 4 seconds before the thread 

 of light had broken the dark ligament or protuberance, by which Venus's limb 

 was united to the limb of the sun, that being the time he estimated the two 

 limbs to be in contact. The internal contacts they think may be relied on; the 

 external happening sooner than expected, occasioned a doubt at its appearance, 

 which made the exact second of its appearance a little uncertain. 



The difference of latitude of the place of observation, north of Middle Point, 

 21.93 miles. The meridian distance of the place of observation, east of Middle 

 Point, 30.6356 miles. 



The latitude and longitude of Middle Point were taken by Messrs, Dixon and 

 Mason, and probably communicated to the r. s. 



Remarks by the Astronomer Royal. — From the data given above, and the 

 length of a degree of latitude, found by Messrs. Mason and Dixon, in these parts 

 = 68.696 English miles, the difference of latitude of Lewestown and the Middle 

 Point above-mentioned, which is the same with the point a, in Messrs. Mason's 

 and Dixon's measure of a degree preceding, is 19' 53"; but the latitude of the 

 point a was found, by Messrs. Mason and Dixon 38° 27' 34"; therefore that of 

 Lewestown is 38° 47' 27" north ; and the difference of its meridian, and that of 

 the point a, or their difference of longitude, is 34' = 2™ ]6» of time, Lewes- 

 town being to the east. But if the difference of longitude of Lewestown east 



4 R 2 



