IV INTRODUCTION. 



Cosmos, vol. 1, remarks on this subject : "Those who have lived for many years in the zone of 

 palms, must retain a pleasing impression of the mild radiance with which the Zodiacal Light, 

 shooting pyramiclically upwards, illumines a part of the uniform length of tropical nights. I 

 have seen it shine with an intensity of light equal to the Milky Way in Sagittarius ; and that, 

 not only in the rare and dry atmosphere of the summits of the Andes, at an elevation of from 

 thirteen to fifteen thousand feet, but even on the boundless grassy plains, the llanos of Vene- 

 zuela, and on the sea-shore beneath the ever clear sky of Cuniana. This phenomenon was 

 often rendered especially beautiful by the passage of light fleecy clouds, which stood out in bold 

 relief from the luminous back-ground." 



It may be well to remark here, however, that the Zodiacal Light has a warm, yellowish tint, 

 unlike the cold, white light of the Milky Way. 



HISTORY OF OBSERVATIONS PREVIOUS TO THESE. 



It seems scarcely probable that a phenomenon, so striking in southern latitudes, could have 

 escaped the attention of early astronomers in those countries; but we meet with nothing in 

 their works of a fully definite and reliable character. We are not to infer, however, from this, 

 that the Zodiacal Light did not exist and shine then, as it does in modern times. Seafaring 

 men have to be ceaseless watchers of the nightly skies ; yet it is very seldom that one can be 

 found who has ever noticed this phenomenon as such, unless his attention has been directed to 

 it in a particular manner, or from some particular circumstance. Its most striking aspects are 

 just before the dawn, or just after twilight, at which time it forces itself on the attention, but 

 is in general supposed to be a part of the crepuscule itself. What I have just said about the mis- 

 takes in our squadron is to the point ; and such facts will also explain the doubts that arose in 

 Cassini's mind, when, in 1683, he first began to notice the Zodiacal Light. He had been pre- 

 viously employed in careful observations of other matters in the same quarter of the heavens, 

 without having at all noticed this phenomenon ; whence he half inferred that it now, for the 

 first time, made its appearance in the sky an inference which subsequent observations and 

 reading led him readily to abandon. 



Kecurring to our theme of the ancient records, it has been thought that Pliny alludes to it 

 under the name of trabes, or the doxou^ of the Greeks, which Hurnboldt, however, supposes to 

 refer to another matter. 



Festus Pompeius notices something of this character, under the terms Acies and Cyparissee. 

 Ammonius, in his life of Charlemagne, A. D. 807, mentions an appearance somewhat like that 

 of the Zodiacal Light; but nothing fully reliable can be found till we come to Childrey's Bri- 

 tannia Baconica* published in 1G61, in which is a clear statement of his having seen it, together 

 with a brief description of its appearance and shape, occupying, however, but a few lines of his 

 book. 



The next observer, and one to whose merit all subsequent writers on this subject have deferred, 

 was Dominions Cassini, an Italian by birth, but, at the time of his observations, attached to 



" "There is another thing which I recommend to the observation of mathematical men, which is : that in February, and 

 for a little before and a little after that month (as I have observed several years together), about six in the evening, when 

 the twilight hath almost deserted the horizon, you shall see a plainly discernible way to the twilight, striking up towards 

 the Pleiades, and seeming almost to touch them. It is so observed any clear night, but it is best iliac noctf. There is no 

 such way to be observed at any other time of the year (that I can perceive), nor any other way at that time to be perceived 

 darting up elsewhere. And I believe it hath been, and will be constantly visible at that time of the year. But what the 

 cause of it in nature should be, I cannot yet imagine, but leave it to future inquiry. Britannia Baconica, 1661, p. 183. 



