56 ESSAYS anp OBSERVATIONS 
or in fome other manner *, - And, after 
all, ic is no more than probable conjec= 
ture, that fuch an alternate acceleration 
_and retardation is brought about by the 
influence of pulfes excited in the ethereal 
medium: Nay, there are fome circumftan- 
ces in thefe phenomena that feem hardly 
intelligible by that hypothefis alone ; as, 
why the intervals of the fits are lefs } in 
denfer mediums; and why they increafe 
fo faft and info intricate a proportion, ac- 
cording to the obliquity {of incidence. 
48. AccoRDING to Dr Bradley’s beau 
tiful theory of the aberration of light, 
the ftars appear to be removed from their 
* For inftance, it might be fuppofed, that every parti- 
cle of light has two contrary poles, like a load-ftone ; the 
one of which is attracted by the parts of bodies, and the o- 
ther repelled ; and that, befides their uniform rectilineal 
motions, the particles of differently-coloured rays revoive 
in different periods round their centre: For thus, their 
friendly and unfriendly poles being alternately turned to», 
wards the furfaces of bodies, they might be alternately dify 
pofed to refletion and tranfmiflion ; and that at different: 
intervals, in proportion to the periods of their rotation, 
+ Newt. optics, book 2. part 3. prop. 17. 
t Prop. 15, ibidem. 
true 
