VOL. LIX.] PHILOSOPHICAL TKANSACTIONS. 64g 



beginning, Mr. S. found of great use ; as he believes he saw the first discernible 

 impression ; he however allowed 2* for the time elapsed between the first percep- 

 tion, and the being sure it was the approach of the moon that affected that part 

 of the sun's limb ; and which latter only could be noted by the clock. The first 

 approach did not however affect the sun's circumference by any thing like a pe- 

 numbra or shade; but began by some asperities of the moon's limb, seeming to 

 thrust themselves into that of the sun ; and which appeared before any conti- 

 nued part of the sun's circumference was cutoff; or perhaps it might be occa- 

 sioned by the first approach of the moon's limb, disturbing the little protube- 

 rances on the sun's circumference, occasioned by the undulation of the air, and 

 which, when rendered exceedingly distinct, appeared almost like the teeth of a 

 fine saw. This whole appearance, to a telescope less distinct, would probably 

 look like a penumbra or shadow. 



Some time before the great spot was im merged, there appeared two parts of 

 the moon's circumference more protuberant than the rest, near the right hand 

 horn ; which so remarkably interrupted the regularity of the curve, that it was 

 taken notice of by all about him ; and which was doubtless occasioned by two 

 mountains on the moon's surface, remarkably higher than the rest ; and he 

 doubts not but the same thing will have occurred to other observers. 



Mr Smeaton was prevented, by clouds, from observing the entrance of Venus 

 On the sun, the evening before. 



XL I. Account of the Transit of Venus over the Sun's Disk, as observed at 

 Norriton, in Philadelphia, June 3, 17 69. By William Smith, D.D. John 

 Lukens, Esq. Surveyor-General ; David Rittenhouse, A. M. ; and John Sellers, 

 Esq. the Committee appointed for that Observation, by the American Philo- 

 sophical Society, held at Philadelphia, for promoting useful Knowledge, p. 289. 

 The above-mentioned gentlemen having provided a variety of excellent instru- 

 ments, telescopes, quadrants, sectors, micrometers, clocks, &c. made all the 

 necessary preparations before-hand, by examining and proving them, and 

 making numerous observations of equal altitudes, Jupiter's satellites, meridian 

 transits, &c., for determining the latitude and longitude of the observatory, the 

 rate and time of the clock, &c. ; and having taken every precaution to observe 

 and secure the times of the contacts, and any other appearance, the first-named 

 three gentlemen, with each a telescope, &c., patiently watched for the com- 

 mencement of the transit ; which, with several other appearances as indications 

 of an atmosphere about Venus, &c. each of these observers recorded separately, 

 and afterwards communicated to each other their notes and observations, which 

 are here all recorded in a very circumstantial manner, unnecessary now to par- 

 ticularize. But the result of the whole was as follows : 



VOL. XII. 4 O 



