iODIACAL LIGHT. 12' 



taut horizon, flitting past the zodiacal light as before a golden 

 curtain. Above these, other clouds are from time to time 

 reflecting the most brightly variegated colours. It seems a 

 second sunset. On this side of the vault of heaven the light- 

 ness of the night appears to increase almost as much as at the 

 first quarter of the moon. Towards 10 o'clock the zodiacal 

 light generally becomes very faint in this part of the Southern 

 Ocean, and at midnight I have scarcely been able to trace a 

 ' estige of it. On the 16th of March, when most strongly 

 luminous, a faint reflection was visible in the east." In our 

 gloomy so-called " temperate" Northern zone, the zodiacal 

 light is only distinctly visible in the beginning of Spring, after 

 the evening twilight, in the western part of the sky, and at 

 the close of Autumn, before the dawn of day, above the east- 

 ern horizon. 



It is difficult to understand how so striking a natural pheno- 

 menon should have failed to attract the attention of physicists 

 and astronomers, until the middle of the seventeenth century, 

 or how it coidd have escaped the observation of the Arabian 

 natural philosophers, in ancient Bactria, on the Euphrates, 

 and in the south of Spain. Almost equal surprise is excited 

 by the tardiness of observation of the nebulous spots in An- 

 dromeda and Orion, first described by Simon Marius and 

 Huygens. The earliest explicit description of the zodiacal 

 light occurs in Childrey 's Britannia Baconica* in the year 



* " 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 to- 

 gether), about six in the evening, when the twilight hath almost 

 deserted the horizon, you shall see a plainly discernible way of 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 nocte. 

 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 con- 

 stantly 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 enquiry." 

 (Childrey, Britannia Baconica, 1661, p. 183.) This is the first view and 

 a simple description of the phenomenon. (Cassini, Decouverte de la Lu- 

 miere celeste qui paroit dans le Zodiaque, in the Mem. de I'Acad., t. viii. 

 1730, p. 276. Mairan, Traite Pliys. de I'Aurore Boreale, 1754, p. 16.) 

 In this remarkable work by Childrey there are to be found (p. 91) 

 very dear accounts of the epochs of maxima and minima diurnal and 



