On the Halo see7i around all Bodies. 23 



the agent through which hght is effective, yet it possesses a pro- 

 perty which hght has not, for it covers the surfaces of black 

 colored bodies, whereas hght is decomposed by them. It differs 

 Hkewise 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. 



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. The phenomena of the interference of light and of the po- 

 larization of light, arise from the peculiar properties which this 

 halo possesses. 



8. Apparently it is only perceptible on the edge of those bodies 

 which are close to the eye in experiment, but iu reality it surrounds 

 and covers every part of the surface. If a 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 

 is on 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 regularly 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 thrown on a screen. 

 But there is still another proof that the different densities of the 

 humors do not produce them. If we hold a steel needle or any 

 bright object horizontally and close the eyehds so as only to ad- 

 mit a small cone of light, and then suddenly 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- 

 tinctly, although the aqueous humor is very perceptible and in 



