138 COSMOS. 



acal light, although tlie night was already perfectly dark. An 

 hour after sunset it was seen in great brilliancy between Alde- 

 baran and the Pleiades ; and on the 18th of March it attained 

 an altitude of 39^ 5'. Narrow elongated clouds are scattered 

 over the beautiful deep azure of the distant 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 colors. It seems a second sunset. On 

 this side of the vault of heaven the lightness of the night ap- 

 pears to increase almost as much as at the first quarter of the 

 moon. Toward 1 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 vestige 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 eastern horizon. 



It is diflicult to understand how so striking a natural phe- 

 nomenon should have failed to attract the attention of physi- 

 cists and astronomers until the middle of the seventeenth cen- 

 tury, or hov/ it could have escaped the observation of the Ara- 

 bian natural philosophers in ancient Bactria, on the Euphra- 

 les, and in the south of Spain. Almost equal surprise is ex- 

 iited by the tardiness of observation of the nebulous spots in 

 Andromeda and Orion, first described by Simon Marius and 

 tluygens. 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 

 af mathematical men, which is, that in February, and for a little before 

 md 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 of the twilight striking 

 up toward 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), 

 Qor 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 

 9f the year; but what the cause of it in nature should be, I can not yet 

 imagine, but leave it to future inquiry." (Childrey, Britannia Baco' 

 nica, 1661, p. 183.) This is the first view and a simple description of 

 the phenomenon. (Cassini, Dicouverfe de la Lumiere C6leste qui pa* 

 roit dans le Zodiaque, in the Mim. de I' Acad., t. viii., 1730, p. 276. 

 Mairan, Traiti Phys. deVAurore Boriale, 1754, p. 16.) In this remark- 

 able work by Childrey there are to be found (p. 91) very clear account* 

 of the epochs of maxima and minima diurnal and annual temperatures, 



