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Pole, returns through Mexico, Loulllana, Canada, 
and the fouthern parts of Greenland, to Drontheirn. 
So that almoft all Africa is deprived of a view of this 
tranfit, and a very confiderable part of Europe. 
If we examine the obfervations of the tranfit in 
1761, in places where there were more obfervers 
than one, and where the contafls were obferved when 
the fun was near the horizon, and at higher altitudes, 
we may fafely conclude that the obfervations will 
be made with fufficient accuracy when the fun is at 
fuch altitudes above the horizon, as not to be greatly 
affeded by the vapours. At the Obfervatory at Upfal, 
when the fun’s altitude at the ingrefs was 34. degrees, 
three obfervers differed 22", whereas at the egrefs, 
when the fun was 44°-4 high, the difference amounted 
only to (>" , It fhould feem, therefore, that obfervers 
ought not to be fent to places where the fun will be 
much lefs than 5° high at the time of either of the 
contads. 
It appears by computation, that the joint effcd of 
the parallaxes both in longitude and latitude to 
lengthen the total duration, will be the greatefl; to 
thofe places which are about 24° or 2 5° to the Eaft 
of Greenwich in the 66th or 67th degree of N. lati- 
tude, when the fun’s altitude is about 5° at each con- 
tad, or if the fun’s altitude at each contad be re- 
quired = 10°, the latitude of places under the fame 
meridian mufl; be 73° or 74* N. In the former cafe, 
this tranfit may be very advantageoufly obferved at 
Tornea°, Kittis, and the adjoining parts of Swedifh 
Lapland} in the latter, at Wardhus, and in the neigh- 
bourhood of the North Cape : for an error of one or 
two degrees either in longitude or latitude will make 
