UPON THE PROPERTIES OF LIGHT. 
257 
the question of interference affecting my own other experiments. First. I observe 
that when one side of a needle or pin is grooved so as to be partly curvilinear, the 
other side remaining straight, we have internal fringes of the form in fig. 21. 
Secondly. It is not at all necessary the pin or other body forming them should be 
of very small diameter, although it is certain that the breadth of the fringes is 
inversely as the diameter. I have obtained them easily from a body one-quarter or 
one-third of an inch in diameter, but they must be received at a considerable distance 
from the body. Thirdly, and this is very material as to interference at all affecting 
my experiments, although certainly the internal fringes vanish when the rays are 
stopped coming from the opposite side of the object, the external fringes are not in 
the smallest degree affected, unless you stop the light coming on their own side ; 
stopping the opposite rays has no effect whatever. Thus, stopping the light on the 
side a (fig. 19), the fringes /y vanish, but not the external fringes c. This at once 
proves there is no interference in forming the external ones. Lastly. I may observe, 
that the law of disposition and polarization in some sort, though with modification, 
affects the internal fringes as well as the external. 
It is a curious fact connected with polarization by inflexion, and which indeed is 
only to be accounted for by that affection of light, that nothing else prevents the rays 
from circulating round bodies exposed to them, at least bodies of moderate diameter. 
If the successive particles of the surface inflected, one particle acting after the other, 
the rays must necessarily come round to the very point of the first flexion. We 
should thus see a candle placed at A (fig. 22) when the eye was placed at B, because 
the rays would be inflected all round ; and even in parts of the earth w here the sea 
is smooth, nothing but the small curvature of the surface could prevent us from 
seeing the sun many hours after light had begun by placing the eye close to the 
ground. This, however, in bodies of a small diameter, must inevitably happen. The 
polarization of the rays alone prevents it, by making it impossible they should be 
more than once inflected on their side which w^as next the bending body, therefore 
they go on straight to C. But for polarity they must move round the body. 
7. It must not be lightly supposed, that because such inquiries as we have been 
engaged in are on phenomena of a minute description and relate to very small 
distances, therefore they are unimportant. Their results lead to the constitution of 
light, and its motion, and its action, and the relations between light and all bodies. 
I purposely abstain from pursuing the principles which I have ventured to explain 
into their consequences, and reserve for another occasion some more general in- 
quiries founded upon what goes before. This course is dictated by the manifest ex- 
pediency of first expounding the fundamental principles, and I therefore begin by 
respectfully submitting these to the consideration of the learned in such matters. 
In the meantime, however, I will mention one inference to be drawn from the fore- 
going propositions of some interest. 
As it is clear that the disposition varies wdth the distance, and is inversely as that 
MDCCCL. 2 L 
