On the Halo seen around all Bodies. Q7 
28. This elongated lens does not, like a round one, give an in- 
verted image of the pin; é only reverses the movements. If a slit 
is cut in a card with a sharp knife, and we look through it ata 
candle or at the clear sky, it will be perceived that the halo is 
present there also, and that its lines are parallel with the slit. On 
moving a pin between the eye and the slit, the shadow of the pin 
will be seen on it, but its movement will be the reverse of the 
true one. In this experiment, as in the preceding one, the shadow 
of the body of the pin is erect, and there is no representation of 
| head. 
29. This contrary motion of object and eeiitende-shie lenticu- 
_ larity—does not belong exclusively to the overlapping of halos 
and to narrow slits, for I have ascertained beyond a doubt, that 
this nebula or halo, which exists on the edges of a// bodies, pos- 
sesses this singular power likewise. Even on the edges of our 
fingers, and between the fingers, as may be ascertained by holding 
up our hand before a candle, and moving a pin between the eye 
and the finger, the halo there seen is an elongated lens, possessing 
one lenticular movement. 
30. But there is a great difference between the halos attached 
to the edges and surfaces of bodies, and those belonging to small 
circular apertures. ‘The circularity, by making the rays of light 
from all the foci of the interstices of the halo converge to one focus, 
and thence radiate, reverses both the image and the movements. 
This circular opening—a pin-hole for instance—is then a true 
lens, with anterior and posterior convex surfaces, the convexity 
of which gives the halo its lenticular or magnifying power. 
31. In whatever manner the lines of this leriticolar halo are 
produced—whether owing to refraction, reflexion, or whether it 
be multiplication of outline—the fact is certain ‘that they do exist, 
and that the halo in which they are seen is‘a true lens. Turn a 
glass globe which way we will, this ‘halo is: ‘always parallel to 
the aa of the surface, and yet the globe has*no edge, nor in 
, is there an edge to any round body, such as a pin or a pen- 
‘p as it appears when close to the eye. 
22 ‘The halo is of a certain depth, and ahwnye: retains its diam- 
= and character, for the dines are forever parallel and the inter- 
“ stices lenticular. Although we are certain from every variety of 
careful experiment, that the lines cross each other in every direc- 
tion, yet after the manner of rays of light, only those lines are vis- 
rte 
aid 
“ty, 
* 
