SSS* PHILOSOPHICAL TRANSACTIONS. [aNNO I76I. 



cording to Mr. Dollond's ingenious invention. This distance was 1' 44|-", at 7** 

 3 1"' 7' apparent time, or 7^ 29™ 15» mean time. Mr. M. remarks, that though 

 Venus's limb and the sun's appeared as well defined as could be desired ; yet 

 when the artificial internal contact of Venus's limb with the sun's was made, in 

 order to measure their distance, Venus's limb alternately dilated itself over, and 

 contracted itself within the sun's limb by a small space. He endeavoured to 

 take it in the middle of this vibration ; but he doubts whether, if the real inter- 

 nal contact had happened at this time, it could have been observed, in such cir- 

 cumstances, to that degree of exactness which Dr. Halley hoped for; and whether 

 on occasion of the next transit, which is to happen 8 years hence, it might not 

 be convenient that the observers should endeavour to place themselves on such 

 parts of the globe, as that they may not see Venus on the sun's body, very near 

 the horizon, but rather when they are both elevated to considerable heights; 

 which will afford them a greater chance of making their observations free from 

 clouds, which usually skirt the horizon, as well as of making them to advantage. 

 Presently after measuring the distance of Venus from the sun's limb, the 

 clouds returned again, and prevented him not only from making any more ob- 

 servations of the same kind, or measuring Venus's diameter, but also, what was 

 of much more consequence, from observing the last internal contact of Venus 

 with the sun's limb, which was the principal observation of all. About 23 mi- 

 nutes after 8 the clouds separated again, and the sun appeared very bright and 

 clear; but there was not the least appearance to be seen of Venus, though he 

 thought himself in a manner sure of observing at least the external contact, as 

 all the calculations make the end to happen much later. 



'^'^Mr. Waddington took the passages of Venus and the sun's limbs across the 

 horizontal and vertical wire of the equal altitude instrument. All the observa- 

 tions which he was able to make are as follow : 



Mean time, in the morning, June 6. 



0's lower limb at horizontal wire. 



9 's centre at vertical wire. 



9 's centre at the horizontal wire. 



9 's preceding limb touches vertical wire. 



9 's subsequent limb at vertical wire. 



0's lower limb at horizontal wire. 



9 's centre at the same. 



0's western and subsequent limb at vertical wire. 

 34 53 0's upper limb at horizontal wire. The observation of this 

 limb of the sun was but indifferent. 

 N.B. As the telescope inverts, the observations, as usual, are set down aa- 

 cording to the appearance. ' 



