380 G. Jones on the Zodiacal Light. 



Arch was seerij all tlirougli the night, spanning the sky. To 

 give only one example of this kind : on the night of the 26th- 

 27th December, 1856, 1 had five observations ; namely, at 7^ 10"^, 

 9^', midnight, at 3 and at 4^ 45"*, mean time. In each of these, 

 the arch was complete across the heavens ; so that each observa- 

 tion overlapped the other considerably. The western horizon^ 

 when I began observing, was only 17^^ 15' from the sun : and the 

 eastern, at my last observation, was but 19*^ : so that, during this 

 night, with the exception of ZQ"^ 16' at the sun, the whole circle 



was complete — its entire completeness being prevented only by 



the smi's superior light. Doubtless the same thing would have 

 occurred every night, but for the moon and clouds. 



^ 2. This is a geocentric ring. The parallelism of the bound- 

 aries of this Luminous Arch at all hours of the night seems to 

 be conclusive on this point. During the nine months of obser- 

 vations the outer boundaries kept their parallelism all through 

 the night, as the eastern skies rose, and as one portion of the 

 heavens after another came into view, or^ in the west, was lost 

 to sight; which could be the case only on the supposition of a 

 geocentric ring. If ^ye make it heliocentric, it must be within or 

 without our earth. If within, then we should not be able to see 

 this light at all at midnight: if without, and the observations 

 were just after nightfall, or before dawn, then w^e should have 

 the end next the sun at a distance of 170 or 190 millions of miles, 

 while the opposite end would be comparatively quite near to us: 

 in which case, by the laws of perspective, the portion towards 

 the sun would be narrowed down almost or quite to the vanish- 

 ing point, while the part opposite to it, or next to us, would be 

 of a great width; all which is contrary to fact as witnessed in 

 these equatorial observations, and is also the very opposite to 

 fact as the Zodiacal Light is seen in latitudes distant from the 

 equator. At New York the Zodiacal Light appears as a cone 

 with its wide part resting on the horizon, and its apex towards 

 the zenith : but if we suppose it to be from a heliocentric ring, 



its apex should be at the horizon and its broad part high up in 

 the sky. 



In the 3d volume of the Japan Expedition Report, I have 



noticed the laws of reflected light as shown by Bouguer: but I 

 must be a^i-----* ^ • - i .t - • ... ^.,. ^n,.r 



observatio 



o ^ 



ence 



-.. .^ .. ..oil known fact in optics that tlie larger the angle be- 

 tween the lines of incidental lidit and of lisrht reflected from any 



object, the larger is the quantity reflected : and Bouguer nas 

 given a table with tlie number of rajs out of a thousand, reflected 

 at various angles from up to 179°. In the diagram on 

 Plate No. 6, of a heliocentric ring, E being tlie earth, and AB 



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