60 Mr. Wilson’s propofed Experiment by 
•upon thefe grounds that we propofe to inquire into the velocity 
of the rays, as they move forward in denfe media fo applied to 
telefcopes. Granting, however, for the fake of argument, 
that light moves down through fuch an unufual telefcope with 
an increafed velocity fuited to the refraCtive denfity of the ine- 
dium, it will hy no means happen, that the aberration will be 
changed on that account. This proportion, which at fir ft view 
may 'appear paradoxical, and even contradictory to what has 
been affirmed above, is however not the lefs certain, and may 
l'erve to fhew, what caution is fometimes requilite in applying 
general principles to particular cafes r for it ffiall be proved, 
that the aberration in fuch a telefcope will precifely agree with 
that of Dr. Bradley’s only in the cafe of the rays moving 
fwifter in the watery medium than in air, in the ratio affigned 
by Sir isaac newton, and that this famenefs of aberration 
will itfelf be a proof of light being fo- accelerated within tlx: 
telefcope. 
In the illuftrations which follow, the reader is fuppofed not 
to be wholly unaccuftomed to the diftinctions betwixt abfolute 
and relative motion, as this will prevent repetitions and all 
unneceflary prolixity. 
Let ABC (tig. i.) be thefphencal refracting furface of fuch 
a telefcope as has been defcribed, and let the telefcope be fup- 
pofed to be at reft, or the velocity of light to be infinite with 
refpect to that of the earth, and let GBMF be aline drawn from, 
a ftar at G, in the pole of the ecliptic, through the center M 
of the refracting furface; the image of the ftar will be formed 
fomewherc, as at F, in the line BF ; and here the interieCtion 
of the crofs wires made ufe of in obl'erving muft be placed. 
It is evident, that the ftar will be feen in its true direction FG ; 
md we muft conclude that to be its true direction, bccaufe we 
know 
