24 WONDER AND MYSTERY. 



diminishing in intensity, when it does so diminish, without 

 the least interruption of continuity. 



The sphere thus is illuminated only in this sense, that 

 an eye in any part of it, turned toward the centre, would 

 see the light ; looking in any other direction through the 

 sphere, it would see nothing. We may, however, conceive 

 such a sphere to be illuminated in another sense, as follows : 



If, for example, the spherical space were filled with dust 

 or smoke, or any other substance consisting of fine parti- 

 cles, and if the light in the centre w r ere increased in intens- 

 ity just enough to make up for the loss that would be oc- 

 casioned by the intercepting of the light by sucli particles, 

 then the space included would be illuminated in another 

 way. The sphere itself would then become visible, just as 

 the sunbeams do when shining through a crevice into a 

 dusty or smoky room, or the rays of the sun when they il- 

 luminate the mistiness floating among the clouds at even- 

 ing in the western sky, and which people call " drawing 

 water," under the erroneous idea that those lines of light 

 are streams of vapor ascending into the air. The effect is 

 produced by the rays of light passing through the inter- 

 stices in the clouds, and then shining upon and being re- 

 flected by the particles of mist which they meet with on 

 the way. It is true that the direction of the illuminated 

 lines is generally downward, as there is usually more mist- 

 iness in the atmosphere near the earth than above, though 

 they are sometimes seen ascending as well as descending, 

 as is represented in the following engraving. 



If now the sphere surrounding the luminous point which 

 I have been describing were illuminated in this manner 

 that is, by having particles floating in the air to receive 

 and reflect portions of the light with a sufficiently in- 

 creased intensity at the source to just make up for the 

 loss, the form and the extent of it that is, of the whole 



