6/4 PHILOSOPHICAL TRANSACTIONS. [aNNO 176Q^ 



which is the boundary between the three lower counties and Maryland, and is 

 situated on Fenwick's Island; the latitude and longitude of this place being accu- 

 rately determined by Messrs, Dixon and Mason. 



The meridional difference of the latitude of the place of their observation, 

 north from Fenwick's Island, at the beginning of the east and west line, as before 

 described, being the easternmost end of the southern boundary between the lower 

 counties and Maryland, is \g' Al" lA'' ; and the meridional difference of longi- 

 tude of the place of observation, west from the point aforesaid, in Fenwick's 

 Island, 5' Ao" of a degree. These data, with the latitude and longitude of the 

 Station point, will determine exactly the place of observation. 



June 2, the weather being clear, had good corresponding observations of 

 the sun. 



June 3, the weather being remarkably fine, they had good observations to set 

 the clock. About 1 2 o'clock they began to direct their glasses to the sun, keep- 

 ing it continually in the field till the time the observation was past. They agreed 

 to watch the telescope one minute in turn, till about 7 or 8 minutes before the 

 contact was expected, lest, by too steady an attention to the glasses, their sight 

 should be impaired, so as to disable them from discerning^ the contact clearly. 

 Mr. Biddle had left his telescope the minute preceding the contact, intending to 

 apply himself steadily to it, from the next minute, till the observation was past ; 

 and when the 48th second was called, he applied himself to the glass, and by the 

 time 3 seconds were elapsed, he perceived, on that part of the sun's limb where 

 he expected the contact, a small impression, which proved to be the limb of 

 Venus in contact with the sun. All the limb of the sun, which appeared at that 

 time in the field of the telescope, had a small undulatory motion, which he ap- 

 prehends was owing to dense vapours, which arose at that place, being near the 

 sea. At Venus's first appearance, it was only like one of those waves on the 

 limb or border of the sun, increased in so small a proportion, that he was doubt- 

 ful for several seconds, whether it was any thing else; thus it continued, making 

 a deeper impression, with that tremulous motion, for about 10 seconds, when 

 the tremor where Venus was in contact ceased, and the indenture was truly cir- 

 cular, with an even termination. 



His absence from the telescope, just before the contact occurred, deprived him 

 of an opportunity of judging whether there was any appearance of an atmosphere 

 preceding the western limb of Venus in contact; but when Venus had entered 

 nearly one half of its diameter into the sun's disk, the observers both saw a lu- 

 minous crescent, which enlightened that part of Venus's circumference which 

 was off the sun, so that the whole of her circumference was visible, but did not 

 continue so until the internal contact; and at the time of the first internal con 

 tact, the eastern or external limb of Venus seemed to be united to the sun's limb 



