On the Halo seen around all Bodies. 23 
the agent through which light is effective, yet it possesses a pro- 
perty which light has not, for it covers the surfaces of black 
colored bodies, whereas light is decomposed by them. _ It differs 
likewise from the magnetic and electric fluid, for with the same 
property of adhesiveness which they possess, it is visible and is not 
confined to a peculiar set of objects. by 
6. Light renders this halo perceptible, according to the : same 
laws which allows us to perceive all other external objects ; “and 
we are not to infer that when it is not visible it does not exist. 
7. This gauzy, misty nebula, when it encompasses lenses or 
- small apertures, has hitherto been designated by the name of frin- 
ges. ‘Ihe phenomena of the interference of light and of the po- 
larization of light, arise from the peculiar properties which this 
0 possesses. 
} 8. Apparently it is only perceptible on the edge of those bodies 
which are close to the eye in experiment, but in reality it surrounds 
and covers every part of the surface. Ifa card be held edgewise, 
close to the eye, the halo, with its lines, will be found to occupy 
the whole extent of plane surface. It is as diaphanous, and as 
permeable to light when it extends over the whole surface, as it 
ison a round or sharp edge. __ 
9. The lines within this halo are not the result of any refrac- 
tive or inflective process of light between the eyelashes or among 
the humors of the eye. That the eyelashes do not in any way 
contribute to their formation can be satisfactorily proved, for on 
looking at the halo on the edge of a bright. object, if we draw 
aside, with our finger, the upper or lower. lid, ‘the shadow of the 
eyelashes will be seen to move regularl across the lines without 
producing the least disturbance or alteration in their position. 
That they do not proceed ‘from the difference in the refractive 
: powers of the humor can also be proved, for they are seen when 
& ~ “the halo is represented through a lens and is thtown on a screen. 
BOs But there i is still another proof that the different | densities of the 
- humors do not produce them. If weshold a a steel needle or an 
, bright: object horizontally and close th ls so as-only to ad- 
-* mita small cone of light, and then sudd enly open them, we shall 
| still perceive the lines within the halo, although the fluid which 
lubricates the conjunctiva, by the contraction of the lids, has ac- 
cumulated in a ridge. We shall see the lines likewise very dis- 
tinetly, although the aqueous humor is very perceptible. ang J in 
3 ee. 4 
