vol.lv.] philosophical transactions. 267 



mum, and will considerably accelerate the times of external contact and ingress. 

 If we suppose the sun's parallax on the day of the transit = 8".7, the horizontal 

 parallax of Venus from the sun will be 2 J ".87; and the times of the external and 

 internal contacts visible in England will be accelerated by the joint effects of 

 parallax, both in the direction of the planet's path and perpendicular to it; the 

 former by 7"" 9^ the latter by 7"" I2^ And therefore Venus will be seen to 

 touch the sun's limb at 7^ 5"^ 47% more than an hour before the time of sun-set; 

 when the apparent altitude of the planet above the horizon will be about 8 deg. ; 

 and the total ingress will happen at 7'' 24"* 40% when the planet's altitude will 

 exceed 5 deg. If the sun's parallax should be one second larger than we have 

 supposed, or Q".7, the time of ingress will happen at 7** 23"^ 51^ These times 

 are not here given with any great degree of confidence: but as the errors in the 

 planet's orbit will, in June i76Q, be nearly the same with those which were ob- 

 served 8 years before, it may be presumed that the foregoing computation will 

 be found not to differ very widely from the truth. 



Having rectified the globe to the declination of the sun at the middle of the 

 transit = 22° 26' 40% and also at the times of the two internal contacts, Mr. 

 H. finds that the whole transit will be visible to a considerable part of Swedish 

 Lapland, the northernmost parts of Asia, and the northern and n. w. parts of 

 North America; for the circle of illumination at the first internal contact passes 

 along the western coast of Africa from Cape Verd, through the straits of Gibraltar, 

 to Clermont in France, leaving Paris about a degree and a half to the west; 

 thence it passes through Germany and along the Baltic Gulf, through Wibourg 

 and Archangel, along the northern coast of Asia; and then traversing the k. e. 

 parts of Siberia, it passes over Japan, enters the great Atlantic ocean, leaves the 

 Marian isles and New 2^aland on the west, and running round Cape Horn, and 

 near Falkland isle, passes on to Cape Verd through the Ethiopic ocean, in a 

 direction nearly parallel to the eastern coast of South America. All places situated 

 under the first part of this line from Nova Zembla towards Cape Horn will see 

 Venus enter on the sun at the time of sun-setting, and at sun-rising under the 

 other half of it. The circle of illumination at the beginning of egress enters 

 Europe to the north of Drontheim in Norway, and crossing the Bothnic and 

 Finland gulfs, passes over Muscovy and the Caspian sea; and running through 

 Persia traverses the Arabian gulf, going southward near the isles of Maldivia, 

 and taking a large circuit towards the south pole, returns through Mexico, Lou- 

 isiana, Canada, and the southern parts of Greenland, to Drontheim. So that 

 almost all Africa is deprived of a view of this transit, and a very considerable 

 part of Europe. 



If we examine the observations of the transit in 1761, in places where there 

 were more observers than one, and where the contacts were observed when the 



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