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XXX V III. An Attempt to determine the 
Height of the Sun s Atmofphere from the 
Height of the Solar Spots above the Suns 
Surface : In a Letter to Mr. J. Ellicot, 
F. R. S. from the Rev . Mr. Horfeley. 
F. R. S. 
' Rea ^ ; -^ ,y 9> 1 Return you many thanks for your 
1 obliging communication of the obser- 
vations of the late tranlit of Venus hy Mayer and 
Rohlius. The phenomena which they relate of the 
atmofphere of that planet are highly curious. They 
were perhaps the more iriteredirig to me, as they 
confirmed fome conjectures of my own, concerning 
the great height of the atmofphere of the fun, and 
of thofe of the two nearer planets. I once attempted 
to make a rough companfon between the height of 
the fun s atmofphere and that of our own, hy com- 
paring the height of the folar fpots above the furface 
of the fun with that of our clouds above the furface 
of the earth, which I did in the following manner. 
The inclination of the Sun’s equator to the place 
of the earth s orbit is fo fmall, that in this enquiry I 
think it may fafely be neglefted; and I confider the 
two planes as one. LetT be the center of the earth, 
S that of the Sun. Join T S, and let dej "be a great 
circle of the fun’s fphere, formed by the interfedtor 
of the plane of the earth’s orbit with the fun’s fur- 
i face. 
