* i 
On the Halo seen around all Bodies. 29 
seen under the trees, and such as appear on a screen or wall, in a 
dark room, when the light comes from a sraall hole in the shutter. 
36. We often see under trees, openings of large size and irreg- 
ular shape; on examination it will be found that they proceed 
from the spaces between leaves that do not hang in dense masses 
like those in the centre. 'These open, irregular spots have their 
inner circumference edged with a rim of smoky light, thus ma- 
king manifest the influence, or rather presence of the halo, for this 
dull light is the representative of it. If we could trace the small 
dense, circular spots to their origin, at the top of the tree, we 
should find that they proceeded from openings as large and irreg- 
ular as those which are reflected from the thinly scattered leaves 
nearer the outer circumference of the tree. Before the light from 
an irregular opening at the ¢op can reach the ground, it will be 
intersected by portions of innumerable leaves which lie in its 
course, until, at last, the aperture through which it makes its final - 
passage is so small in size as nearly to admit of a continuity of 
halo. Therefore, let the outline of an aperture be what it may; 
provided it be not of so large a diameter as to prevent the micro- 
scopic, or lenticular action of the halo; the rays of light will con- 
verge to a point, the central rays “ which will throw on the 
ground or floor, a dense round mass of light, such as is called an 
image of the sun, and the divergent rays will throw an inverted 
image or shadow on the screen or wall. That some of the dense 
light spots are of an oblong form is owing to the obliquity of the 
sun’s rays, or to the oblique a of the apertures with regard 
to the rays. 
37. The halos of two objects of ES will be of 
double density when they overlap » one another. This experi- 
ment can be made by bringing them. together with their edges 
perfectly parallel. The halos of three or four pins when placed 
behind one another, will be so dense, that. objects beyond them 
will appear very indistinct, whereas through one halo every thing 
is acct rately seen, two dimly, through five or six, not at 
38. ‘Light, like all other matter, is less permeable as it becomes 
more dense. When it is concentrated, the feebler rays which 
* emanate, or are reflected from objects behind it, are lost in the 
intensity of the mass through which they seem to pass in order 
to reach our eye. The concentrated density of light is the true 
