15S Dr Wollaston on the Finite Extent of the Atmosphere. 
of. an unlimited expansion of an atmosphere, and finding that no 
such effects are exhibited in any of the bodies of the planetary 
system^ he concludes that these bodies have not an atmosphere 
of indefinite extent ; that the earth’s atmosphere is also limited, 
and consequently, that matter has a finite divisibility, and that 
the doctrine of ultimate atoms is thus indirectly established. 
If the expansion of any atmosphere is unlimited, the same 
kind of matter must pervade all space, and the sun, moon, and 
all the planets must have this matter condensed around them in 
quantities dependent on the force of their respective attractions. 
For the purpose of determining if such an accumulation of mat- 
ter does exist round any of the planetary bodies, he begins with 
the Sun^ which, on account of its having the greatest mass, 
ought to accumulate round it the greatest quantity of atmosphe- 
rical matter. 
Assuming the sun’s mass as 330,000 times that of the earth, 
and his radius 111.5 times that of the earth, he finds that the 
distance from the sun’s centre at which his atmosphere will have 
a density fully equal to our own, and therefore capable of re- 
fracting a ray of light more than one degree, is = VS30,000 = 575 
575 
times the earth’s radius, = = 5.15 times the sun’s radius ; 
that is, a point whose angular distance from the sun’s centre is 
15' 49" X 5.15 = 1° 21' 29". 
Now, if any of the planets or stars, in approaching the sun’s 
disc, suffer no refraction at all, when carefully observed at the 
above distance, or at less distances from the sun’s centre, we may 
safely conclude that no such atmosphere exists. 
In order to determine this point. Captain Kater made a se- 
ries of observations on Venus on the 18th and 19th of May 
1821, when she was on the eve of her conjunction with the sun, 
and Dr Wollaston made similar ones after her conjunction. 
Captain Rater’s last observation was made when Venus was only 
65' 50" from the sun’s centre ; and Dr Wollaston’s when her dis- 
tance was only 53' 15" ; and at both these times, neither her 
motion nor her position were in the least affected by a solar at- 
mosphere. . In 1805, M. Vidal of Montpellier observed 
when her distance from his centre was only 46', and Mercury 
