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 tha light comes from a small 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 top 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 of 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 position of the apertures with regard 

 to the rays. 



37. The halos of two objects of slender diameter 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 owe halo every thing 

 is accurately seen, through tivo dimly, through five or six, not at 

 all. 



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 



