68 Mr. Wilson’s propofed Experiment by 
paffes along the axis. By prop. A. therefore, the velocity of 
the ray, whatever this may be after refraCtion, muff be to that 
velocity by which it would have moved relatively in the axis, 
fo inclined to its path, previous to the refraction, inverfely as 
the lines of incidence and refraCtion. Now this being duly 
eonfidered, it will be found that the velocity within the me- 
dium, cor refpon ding to this fuppofed aberration, or the abfo- 
lute velocity within the medium, mult be to the velocity within 
the medium correfponding to the Bradleyan aberration, inverlely 
as the tangents of thefe two angles : for let V and v exp refs the 
velocities before and after refraction correfponding to the Brad- 
leyan angle, and X and x the velocities before and aftei cone- 
fponding to the fuppofed uncommon angle, * being the aCtual 
velocity after refraCtion ; then, becaufe by prop. A. the ante- 
cedent is to the confequent, in both cafes, in the fame ratio, 
•viz. as the fine of refraction to the fine of incidence, it will be 
V : v :: X : x, and therefore V X :: v : x. But from the 
nature of the aberration V mult be to X (this luppofititious 
velocity before incidence) inverfely as the tangents of the 
angles of the two aberrations. This therefore muft be the 
ratio of v to But v is given as before Ihewn ; therefore at 
the velocity within the medium correfponding to the fuppofed 
obferved aberration is alfo given, and by the fame rule as was 
found formerly in the cafe of the firft telefcope. 
What has been at prefent advanced is unconnected with any 
hypothetical notions concerning the rays or the caufe of refi ac- 
tion. Light has been considered only as fomething which moves 
uniformly from one place to another, and which is always re- 
fraCted according to a known law. The firft of thefe properties 
has been put beyond all doubt by the obfervations of Dr. 
Bradley and Mr. molyneux ; and it is has been long known 
that the laft is quite agreeable to experience. 
