92 
Dr. Wollaston on the 
which has the greatest power, and see whether even there 
the non-appearance of those phenomena which might be ex- 
pected from such an atmosphere, will warrant the inference 
that our own is confined to this one planet by the limit set to 
its divisibility. 
By converse of the same rule which gives an estimate of 
extreme rarity at the moon’s surface, we may form a con- 
ception at what distance round the sun refraction from such 
a cause should be perceived. If we calculate at what appa- 
rent distance from the body of the sun his force is equal to 
that of gravity at the surface of the earth, it is there that his 
power would be sufficient to accumulate ( from an infinitely 
divisible medium filling all space) an atmosphere* fully 
equal in density to our own, and consequently producing a 
refraction of more than one degree, in the passage of rays 
obliquely through it. 
If the mass of the sun be considered as 330.000 times that 
of the earth, the distance at which his force is equal to gra- 
vity will be 1/330.000, or about 575 times the earth’s radius; 
and if his radius be 111,5 times that of the earth, then this 
distance will be -&L or 5.15 times the sun’s radius; and 
hi . 5 ^ u 5 
1 5 / 49 /; * 5 ’ 1 5 = 1 ° 2l ' 29", will he the apparent distance from 
the sun’s centre on the 23d of May, when the following ob- 
servations were made. 
What deduction should be allowed for the effect of heat, 
* Such an atmosphere would, in fact, be of greater density on account of the far 
greater extent of the medium affected by the solar attraction, although of extreme 
rarity ; but the addition derived from this source, may be disregarded in the present 
estimate, without prejudice to the argument, which will not be found to turn upon 
any minute difference. 
