[ J 
a charge fo great, as not to have more than a geome- 
trical minute of the fun’s apparent diameter vifible at 
once. 
Since the fun is an object fo very remote, the pen- 
cil of rays flowing from the center of its difk, and 
incident all over an objedt-lens (tho’ it fhould be a 
foot broad) would not differ fenfibly from a perfect 
cylinder within the diftance of above ioo miles from 
its bafts at the lens ; tho’ in reality the whole pencil is 
an acute cone, whofe angle at the vertex is almoft 
evanefcent. 
Hence it follows : 
That if the two poles of two equal objedb-glafles 
are placed at the diftance (fuppofe) of a foot from 
one another, the two centers, c, v , of the two folar 
images muft, as to fenfe, remain always at that very 
fame diftance {viz, i foot) from one another, tho’ 
the fun lhould be placed ten times as far off as it now 
is: but fince the fun’s greater diftance would diminifh 
the diameters of both of the folar images ; m n , added 
to rs , muft be the true difference of the apparent dia- 
meters of the images (and alfo of the fun) at dif- 
ferent times. 
According to Mr. Azout ( Harris's Lexic. Tech??. 
VclA. fee Su n), the apparent diameter of the fun 
never exceeds 32' 45"; whence its radius never ex- 
ceeds i6 / 2 2 7 30''' ; the tangent whereof is about 
476,328 (if I miftake not) to the radius 100,000,000. 
As the faid tangent : to the faid radius : : fo half an 
inch : to 1 04.96 inches, and decimal parts. 
According to this, 
If the focal length of a lens is 104.96 inches and 
parts, it cannot collect the fun’s rays to a lefs focus^ 
Y at 
