18 ESSAYS anp OBSERVATIONS. 
\ 
with the freedom and perpetuity of the 
celeftial motions *. 
7. Some have thought, that, if the par- 
ticles of light repel one another, theirmu- 
tual perturbation may be prevented: Bac 
the contrary is manifeft upon the leaft re-, 
fle&tion ; for tho’, by that means, the par- 
ticles might be prevented from ftriking, 
they muft inftantly turn one another from 
their rectilinear courfes, as foon as they 
come, in different directions, within the 
reach of their mutual powers. "Thus, we 
find by experience, it is impofhible to make’ 
one ftream of air penetrate another with- 
out confufion ; for-thetwo ftreams either 
unite into a common one \with an inter~ 
mediate direction, or produce irregular 
eddies. 
8. HERE, by the bye, we may feethat 
the ingenious fyftem of Bofcovich, the 
Roman profeffor, concerning the elements 
of matter +, whatever may be faid for it 
froin other confiderations, gives us no af- 
fifta nce 
* See his Nova theoria Jucis et colorum. 
+ See his Differt- de lumine et de viribus vivis, 
