INTRODUCTION. 



APPEARANCE OF THE ZODIACAL LIGHT. 



To PERSONS not familiar with the subject of this work, it may be proper to state, that, what 

 is called the Zodiacal Light, is a brightness which appears in the western sky after sunset, and 

 before sunrise in the east, following nearly or quite the line of the ecliptic in the heavens, and 

 stretching upwards to various elevations, according to the seasons of the year. It has been 

 called by this name, from the fact that it was formerly thought to confine itself within the limits 

 of the zodiac. It appears to best advantage when the ecliptic makes its highest angle with the 

 spectator's horizon; at which times, in moderate latitudes, it reaches to his zenith or beyond it, 

 having near the horizon a striking brilliancy, and thence fading upward, mostly by impercep- 

 tible degrees, till, at its vertex, it can be made out only by a careful and experienced eye. As 

 those seasons advance when the ecliptic is declining gradually towards the horizon, the Zodi- 

 acal Light fades away, till it is perhaps entirely lost, or can be seen only by those who have 

 followed it, in its changes, night after night, and are thus able, by familiar acquaintance, to 

 detect and trace its dim markings on the sky. 



In our high northern latitudes, it can be seen with difficulty, or at least can be made out 

 unsatisfactorily, through a large portion of the year ; while at the European observatories, 

 most of them still further north, it is generally very obscure; and observers in these countries 

 have, therefore, been discouraged from attention to a subject for which their circumstances are 

 so little favorable. In the lower latitudes, however, and especially in those near the equator, 

 it lias often an exceeding brilliancy at the horizon, ascending from this, a striking object, far 

 into the sky; and I have in several instances known ike reveille to be beaten in our ships, evi- 

 dently from mistaking the Zodiacal Light for the dawn. I remember, on one occasion, when in 

 the " Mississippi " during her late cruise, we had sighted the light-house of Point du G-alle, in 

 Ceylon, in the evening, and the ship was ordered to be kept lying off till the morning would 

 permit us to enter the harbor, word was passed for the "officer of the deck to send for the 

 captain and first lieutenant at early dawn." I was on deck in the morning at my observa- 

 tions, a few minutes after four o'clock, when the lieutenant on duty came up to me and said : 

 "Don't you call this early day-light?" I answered "No, it is not day-light yet." "Why," 

 he said, "what do you call this over here?" pointing to the Zodiacal Light, which was show- 

 ing itself with an effulgence that might very easily lead to such a mistake; though it wanted 

 yet more than half an hour of the earliest dawn. See also the close of my record No. Ill, 

 where it is noted that, at two hours after sun-set, I overheard one of the quartermasters, as he 

 was looking at the Zodiacal Light in the west, remark to another: "If that was not in the 

 wiong part of the sky, I should say that the sun was just going to rise there!" Humboldt, in 



