5g6 PHILOSOPHICAL TRANSACTIONS. [aNNO I76I. 



/jXI. Latitude of the Observatory at the Cape of Good Hope reduced from the 

 Observations oj different Stars. By Mr. Charles Mason, p. 395. 



The latitude is here deduced from observations of 10 remarkable stars, the 

 mean of all being 33^ 55' 42" south. 



LXII. An Observation of the same Transit of Plsnus over the Sun, June 6, 1761, 

 at Madras. By the Rev. William Hirst, Chaplain of one of his Majesty*s 

 Ships in the East Indies. Dated Fort St. George, July l, 1761. p. 396. 



Mr. Hirst began to make observations for regulating his clock near 3 weeks 

 before the day of the transit, by taking equal altitudes first, and then by meridional 

 passages of Spica virginis, and of the sun ; so that there can be no doubt as to 

 the accuracy of his time. The place of his observation was fort St. George, on the 

 top of the governor's house, the latitude, as determined by many observations 

 made not long before, with an excellent quadrant, Mr. Hirst says is 13° 8' n. and 

 and he makes it 3™ 4^ of time eastward of Pondicherry. The telescope was a re- 

 flecter 2 feet long, made by Mr. Adams, of Fleet-street, London. 



Sometime before 5 in the morning of the 6th of June, Mr. Hirst and the rest 

 of the gentlemen, met on the terrace of the fort-house, and were at their glasses 

 at the time the sun rose, lest Venus might enter the disk before the time cal- 

 culated by the astronomers. The Jesuits had calculated the beginning for 

 Pondicherry, at 6*^ 57""- The London calculations, reduced to the meridian of 

 fort St. George, gave it at 7^ 26"^ 35% apparent time. 



The morning proved favourable to the utmost of their wishes, which the more 

 increased their impatience. At length as Mr. Hirst was stedfastly looking at the 

 under limb of the sun towards the south, where he expected the planet would 

 enter, he plainly perceived a kind of penumbra, or dusky shade : on which he cried 

 out, 'tis a-coming, and begged Mr. Call to take notice of it. Two or 3 seconds after 

 this, namely, at 7^ 31™ l(y apparent time, happened the first exterior contact of 

 Venus with the sun, which all the 3 observers pronounced at the same instant as 

 with one voice. Mr. Hirst is apprehensive that to be able to discern an atmo- 

 sphere about a planet at so great a distance as Venus, may be regarded as chime- 

 rical ; yet he affirms that such nebulosity was seen by them without presuming 

 to assign the cause. They lost sight of this phenomenon as the planet entered 

 the disk, nor could Mr. Hirst perceive it after the egress. The total ingress, or 

 first internal contact, was determined with a precision equal to that of the first 

 external contact, at 7*" 47"™ 55* apparent time. 



Mr. Hirst thinks it necessary to take notice of another odd phenomenon. At the 

 total immersion, the planet, instead of appearing truly circular, resembled more 



