554 PHILOSOPHTCAL TRANSACTIONS. [anNO I76I. 



and satisfaction ; and another reflector of 2 feet focus, with an achromic object- 

 glass micrometer of 40 feet focus, being the same sort of instrument with those 

 that were made, by order of the r. s., for Dr. Bradley, at the Royal Observatory 

 at Greenwich; and for Mr. Maskelyne, who went to St. Helena; and Mr. 

 Mason, who went to Bencoolen ; diiFering in one particular from their instru- 

 ments, which had only a common object-glass micrometer. 



They had no sight of the sun till a quarter of an hour before 6 o'clock, when 

 through an opening, which lasted for about 2 minutes. Dr. Blair, Dr. Bevis, 

 and Mr. S. plainly and distinctly saw Venus on the sun, and concluded that she 

 was then considerably past the middle of her transit. About a quarter after 6, 

 Mr. S. made the first observation, which was, in measuring the diameter of 

 Venus; and soon after he measured her distance from the sun's limb, in the 

 direction of a line going through the sun's centre ; and so continued measuring 

 in the same manner, and sometimes measuring the diameter of Venus, till near 

 the internal contact; only about a quarter after 7, he measured the distance of 

 Venus from the sun's limb, in a supposed direction of her transit line, or path 

 over the sun. 



About half an hour after 7 the clouds dispersed, and they had the sun perfectly 

 clear during the remainder of the transit. When Venus approached the inter- 

 nal contact, Mr. S. took off the micrometer, and changed the magnifying power 

 of the telescope, which during the measurements had been that of 70 times, 

 into another of 140 times, and with this magnifying power he observed the in- 

 ternal contact; in which he thinks he cannot have erred so much as 2 seconds, 

 for the air was extremely clear, and at rest. With the same magnifying power 

 he observed the total exit; and does not think he erred in this above 5 seconds, 

 though this is a more uncertain observation than the former, and can by no 

 means be determined so accurately as the internal contact; and what he erred in 

 this last observation is rather in excess, in making the exit too late. 



Times and measurements taken at Savile-house, June 6, 176 J. Mr. Short 

 observing, and Dr. Bevis marking down the times. 



Internal contact by Mr. Short, through a reflector of 2 feet focus, magnifying 

 140 times 8*^ IS"" 21*^ 



Total exit by Dr. Blair, through a reflector of 1 8 inches focus, 

 magnifying 35 times 8 36 12^ 



Total exit by Mr. Short, through a reflector of 2 feet focus, mag- 

 nifying 140 times 8 37 05^ 



The diameter of the sun in a horizontal direction was measured just after the 

 transit, and found to be = 31' 30.8*. The clock at Savile-house was several 

 times compared with Mr. S.'s clock in Surry-street, from Friday evening the 5th 



