352 THE POPULAR SCIENCE MONTHLY. 



sible gradations until it becomes too feeble for distinct vision. Its aspects vary 

 very much with the season of the year." 



The crepuscles, or streaks of light from the sun, must not be mis- 

 taken for the zodiacal light ; the former are sometimes visible between 

 twilight and dark, the latter not until the shades of night have fully 

 set in. Neither must the milky-way be mistaken for it by inexpe- 

 rienced observers, as the zodiacal light has a warm yellowish tinge 

 unlike the cold white light of the milky-way. 



Having endeavored to open the way for a consideration of the 

 subject, we will now proceed to give a history of former observations. 



There is no mention of any appearance of this light by very early 

 writers. There is mention of Arcturus and the bands of Orion in the 

 book of Job, and the constellations of the zodiac were assigned names 

 at a very early date. The zodiacal belt was in use among the ancient 

 Egyptians and Hindoos. If this light had been visible, it is highly 

 probable some ancient writer would have spoken of it. Our author 

 observes : 



"It is scarcely probable that a phenomenon so striking in southern latitudes 

 should have escaped the attention of early astronomers in those countries, but 

 we meet with nothing in tlieir works (referring to it) of a fully definite and re- 

 liable charactei*." 



He is, however, of the opinion that it may have been overlooked 

 or mistaken for the crepuscle at early dawn or twilight. 



It has been supposed that Pliny, who wrote in the first century 

 of the Christian era, alludes to it under the name of trabes or the doKovg 

 of the Greeks, but Humboldt thinks that Pliny refers to another mat- 

 ter. 



Ammonius, in his life of Charlemagne, a. d. 807, mentions an ap- 

 pearance somewhat like the zodiacal light, but there was no reliable 

 notice of it before it was described in Childrey's " Britannia Baco- 

 nica " in 1661, which gives a brief description of its appearance and 

 shape. The reference to it may be found in that work, at page 183. 



It was reserved for Cassini to direct attention to its examination 

 for the first time with earnest inquiry and interest. His first notice 

 of it was on the evening of tlie 18th of March, 1683, He was watching 

 in the west for other things, but was struck with the appearance of this 

 luminous streak reaching far up in the sky. Like most discoverers, 

 Cassini immediately formed a theory in regard to it after making but 

 ten observations. This hypothesis, based on very insufficient data, 

 has continued to the present time to influence the opinions of astrono- 

 mers, and has retarded interest in observing its phenomena. Like 

 most theories of the heavenly bodies in their first origin, it was doubt- 

 less erroneous, and, like the Ptolemaic theory of the solar system, it 

 has materially interfered with the establishment of a correct knowl- 

 edge of what is the truth. 



