20G 
rays, which caused them, in their passage through 
any refracting substance, to be alternately reflected 
or transmitted, at equal intervals, for many vicissi- 
tudes ; and the returns of these dispositions in the 
rays, he named fits of easy reflection or transmis- 
sion. Of what kind, however, this action or dispo- 
sition in the rays may be, he does not inquire ; but 
suggests the possibility of its depending on a vibra- 
tory motion, excited in bodies by the rays which 
impinge on them. But whether this hypothesis be 
true or false he does not consider, contenting him- 
self with the bare discovery, that the rays of light 
are, by some cause or other, disposed to be reflected 
or refracted for many vicissitudes *. 
481. As thus, the mechanical hypothesis, even in 
the hands of Newton, seems to fail in assigning the 
cause, why light is variously refracted and reflected 
by bodies, we may, perhaps, be permitted to specu- 
late on the facts and analogies, which the late disco- 
veries in the elementary constitution of bodies, and 
in the nature of light, suggest to us ; and try whe- 
ther they will conduct us a step farther in the inves- 
tigation of this intricate subject. " Prudens interro- 
gatio," says Lord Bacon, " est dimidium scientise. 
Vaga enim experientia, et se tantum sequens, mera 
palpatio est, et homines potius stupefacit quam in- 
format." 
482. From the view which has been given (440, 
et seq.) of the nature and composition of solar light, 
it appears, that although, in many of their physical 
* Optics, B. i. part. 3. prop. 12.' 
