Diftance, Magnitude, &c. of the Fixed Stars, &c. 53 
which was fuppofed to revolve about it as a fatellite, for want 
of fufficient magnitude in the body from whence it was emit- 
ted, fhould fuffer no fenfible diminution at all. Placing then 
the line, in which the two faces of the prifm would interfe& 
each other, at right angles to a line joining the two ftars; if 
the thinner part of the prifm lay towards the fame point of the 
heavens with the central ftar, whofe light would be moft turned 
out of its way, the apparent diftance of the ftars. would be in- 
creafed 2”. 53’”’ and confequently become 3”. 53’” inftead of 1”, 
only, the apparent diftance fuppofed above in art. 21. On the 
contrary, if the prifm fhould be turned half way round, and 
its thinner part lye towards the fame point of the heavens with 
the revolving flar, their diftance muft be diminifhed by a like 
quantity, and the central ftar therefore would appear 1”, 5 3’”’ dif- 
tant from the other on the oppofite fide of it, having been removed 
from its place near three times the. whole diftance between them. 
34. Asa prifm might be made ufe of for this purpofe, which 
fhould have a much larger refracting angle than that we have 
propofed, efpecially if it was conftructed in the achromatic 
way, according to Mr. poLLonp’s principles, not only fuch a 
diminution, as one part in twenty, might be made ftill more 
diftinguithable; but we might probably be able to difcover , 
confiderably lefs diminutions in the velocity of light, as. per- 
haps a hundredth, a two-hundredth, a five-hundredth,. or everx 
a thoufandth part of the whole, which, according to what 
has been faid above, would be occafioned by {pheres, whoie 
diameters fhould be to that of the fun, provided they were of 
the fame denfity, in the feveral proportions nearly of 70, 50, 
30, and 22 tor re{pectively. 
35. If fuch a diminution of the velocity of light, as that 
above fuppofed, fhould be found really to take place, in confe- 
qence 
