356 THE POPULAR SCIENCE MONTHLY. 



would emit a light of the same intensity the whole way from the base 

 to the apex. But another law of optics, that the strength of light is 

 inversely as the squares of the distances of the object affording the 

 light, would here make its application ; and this ring, at our zenith, 

 being by that supposition about 140,000,000 miles nearer to us, than 

 at the base, we should then have the zodiacal light far more intense 

 at the apex than at the base ; all of which is entirely opposite to the 

 facts of the case. 



He offers, now, as a last conclusion, the hypothesis of a nebulous 

 ring with the earth for a centre. He makes certain deductions from 

 the examination of the preceding theories. 



"They are 1. That the substance giving us the zodiacal light must be 

 equally near to us in all its parts, inasmuch as the lateral changes of the light, 

 i. e., the changes of boundaries, have a uniform character and mostly a parallel- 

 ism in their whole extent from apex to base ; 2. That no part of this substance 

 can be very remote from us, inasmuch as the outlines of the Mght were clearly 

 and sensibly affected by my own position on the globe, and even by my change 

 of position in a single night ; and, 3. That the laws of reflected light require an 

 arrangement or a shape of this nebulous matter which will give us, at the base 

 of the zodiacal light, larger angles between the lines of the incident and re- 

 flected light than at other portions, and also a regular decrease of such angles 

 from the base to the apex of the light, as produced by such a shape. These 

 three requirements appear to.be fully met by an hypothesis which, if the theo- 

 ries examined are untenable, is now the only one remaining to us. 



" The hypothesis is that the zodiacal light is a ring around the earth. 



" The thought is a somewhat startling one, yet startling only from its novelty ; 

 for it is entirely in accordance with what we know of our sister planet (Saturn), 

 and also with the whole of Laplace's celebrated theory of the formation of 

 globes." 



We will not take up time and space with quoting his application 

 of that theory in explaining some of the phenomena of this light. 



Avoiding the consideration of these topics, we will proceed to apj^ly 

 the result of Bouguer's experiments on reflected light to this case. 



In the annexed diagram he takes an observation made on the 4th 

 of September, 1854, as an example, for the reason that it is a simple 

 one, and one also in which the spectator is near the plane of the eclip- 

 tic. It was made in latitude 22 18' north, longitude 114 10' east. 

 The sun rose at 5^ 48". The stronger light was at S'' SO'" to 4'' SO"", 

 the diffuse light at S*" 45'. Sun's longitude 161 35'. The horizons at 

 4'' 30", S*" 30", 2'' 30", and l*" 30", and at midnight, are given, together 

 with the line of the spectator's vertices, as well as his positions O, o, etc., 

 at 4^ 30" and S** 30". A, B, C, F, are the boundaries of the zodiacal light 

 at 4'' 30", and E, F, G, at S*" 30" ; the apices C and G are carried a lit- 

 tle above the more condensed portions of the ring; but the reader is 

 at liberty to suppose them to be at any other part, as he may think 

 best. The direction of the sun is given ; and S', S", S'", S"", S'"", are 

 supposed to be rays of light proceeding from that luminary. 



