Page:Littell's Living Age - Volume 127.djvu/588

576 world; but their members have no right to slay except in strict self-defence, of which, we suppose, but suppose very reluctantly, the taking of food for payment must be held to be part.

 

 . — During his residence in the island of Jamaica in 1863 and 1869, M. Houzeau assiduously observed the zodiacal light for six months consecutively, and has now communicated the results to the Belgian Academy. M. Houzeau has for more than thirty years devoted great attention to this puzzling phenomenon, and he is fortunate in having now obtained such a fine series of observations, the boundary of the zodiacal light having been carefully determined by him on 56 nights out of the 179. As far as these results go, it appears that the zodiacal light is not appreciably inclined to the ecliptic, and does not approach to coincidence either with the plane of the sun's equator, as Cassini supposed, or with that of the moon's orbit, as Jones has more recently suggested. The slight observed deviations from the plane of the ecliptic are explained by M. Houzeau as results of the greater absorption of the light of the lower or southern side by our atmosphere, which is, of course, less transparent near the horizon. From these observations M. Houzeau concludes that we must reject both the hypothesis which regards the zodiacal light as an appendage of the sun, and that which assigns it to the moon; and since, if it were a ring round the earth, it would be seen as a complete arch in the sky crossing from east to west, the author is driven to the conclusion that it is a fan-shaped sector, somewhat similar to the tail of a comet, spreading from the earth towards the sun, thinning off on each side of this direction, so that it extends to about 40° on the side towards which the earth is moving, and 60° or 70° on the other side. This must, of course, be modified if we accept those observations in which the zodiacal light has been distinctly traced right across the heavens from east to west; but M. Houzeau's conclusions are founded on his own observations alone. For the period of his watch there was a sensible diminution of brightness, the zodiacal light being seen in January, 1869, as readily as a fourth-magnitude star in twilight, whilst by June it was not so bright as the fifth magnitude.

From observations on his voyage to Rodrigues and back with the transit-of-Venus expedition, Mr. Burton has been led to very different conclusions. He was provided with a binocular spectroscope devised by himself specially for this work, and with this he determined the spectrum of the zodiacal light to consist of a continuous band with a bright line in the yellow (forming the boundary of the spectrum on that side) and a dark line in the green. This same spectrum was given by every part of the sky unoccupied by the milky way, a most important observation which, in combination with the change of form of the zodiacal light seen when the observer passed from S. to N. latitudes, shows, according to Mr. Burton, that it reaches and probably surrounds the earth. From the spectrum seen, as well as from the fact of polarization in a plane through the axis of the zodiacal light, Mr. Burton further concludes that it is emitted by matter partly liquid and partly solid, intermixed with gas.

The observations made by Signor Arcimis at Cadiz, and published in the Memorie degli Spettroscopisti Italiani, agree on the whole with those of Mr. Burton. With a Hoffmann spectroscope Signor Arcimis observed a bright line in the greenish yellow midway between D and E, whose position he fixed at 1,480 of Kirchoff's scale, and another in the blue beyond F, at about 2,270 of the same scale. The former may very possibly be identical with the bright line in the spectrum of the corona, which is at 1,474 of Kirchoff's scale; and Signor Arcimis thinks that the line in the blue may turn out to be one of the bands of carbon seen in the spectra of comets. If these surmises are correct a very important connection would be established between these bodies. Signor Arcimis makes no mention of the dark line in the spectrum of the zodiacal light seen by Mr. Burton, but it is quite possible that a bright line in the blue might produce by an effect of contrast the appearance of a dark line on the green side of it, or vice versâ, it being difficult at the faint extremity of a spectrum to distinguish the two cases. Academy..