INTRODUCTION. XI 



from our excellent little globe. By laying folds of paper below this, and sticking pins through 

 the stars, I multiplied the charts, till, after nearly a year's work in this manner, I was able to 

 have the chart cut in wood at Canton, and thus I found myself well prepared for work. My 

 custom was, at evening, to watch for the earliest appearance of the Zodiacal Light; and, as soon 

 as I could get reliable boundaries, to notice their course among the stars, and draw these bound- 

 ary-lines on the chart, with such annotations as the case might require; then, again, after the 

 interval of half an hour or an hour, to go out once more, and as the boundaries would be 

 changed in that time, to take the new ones in a similar way; and so proceed till the Light could 

 be no longer seen: and thus also, in a reverse order, in the morning. And after having once 

 fairly commenced say about the first of March, 1853 I never failed for one evening or morn- 

 ing, (Sundays always excepted,) till our reaching home on the 22d April, 1855, to see, and, 

 with one exception, to make record of the Zodiacal Light, when the moon and clouds did not 

 interfere to prevent. In the case of that one exception, I saw the Light; but being shut up 

 among the houses in Canton, I could not get reliable boundaries. 



The development of facts in the Zodiacal Light came upon me gradually, and, before they had 

 disclosed themselves, much valuable time in the high southern latitudes, at the early part of 

 our cruise, was lost; on our return, however, we went still further to the south, and I was able 

 to make amends in some measure for this loss. 



There is no mention made, in any books on the Zodiacal Light, of any differences in the Light 

 itself;* but I very soon began to notice that there was a Stronger Light at the central part, or 

 along the axis ; while, beyond this., on either side, and also above, a dimmer kind of light ex- 

 tended itself, as if the matter giving us this light was more condensed at its central parts, and 

 was thinned out beyond. I have called these the Stronger and the Diffuse Light, and have 

 marked the boundaries of the former on my chart by full lines, while the bounds of the Diffuse 

 are designated by lines of dashes, each having the hours of the observation affixed to it. Some- 

 times, beyond the Diffuse Light, there was also what seemed to be, not a positive light, but 

 rather as if the sky were slightly paled (if the reader will allow the word) ; so slightly, that 

 I could not trust my own sight respecting it, till I had called in repeatedly the aid of other 

 persons (see chiefly June 27th and July 1st to llth, 1853). I have marked the boundaries of 

 this last by dotted lines ; but I consider it only as the more Diffuse matter greatly attenuated 

 at its outer edge, which, by the sinking of the ecliptic towards the horizon, was now brought so 

 as to make its reflection visible to us. In the case just referred to that of July it presently 

 changed into the Diffuse Light itself. The Stronger Light is evidently the one of which 

 Cassini has given the boundaries in his written accounts. 



It is not to be supposed by the reader that any of these kinds of light was bounded by sharp 

 lines easily detected in the sky. On the contrary, the Stronger passed by degrees into the Dif- 

 fuse, and the latter also gradually faded away. Yet there was, in the former case, a line of 

 greater suddenness of transition, which, when my eye had got accustomed to observations, I 

 was generally able to make out without much difficulty ; and this is the line or the boundary 

 which is given in my charts. The outer boundary of the Diffuse Light was also tolerably well 

 marked. That I was not fanciful in this, is shown by the frequency with which other persons 

 on board, both officers and seamen, when requested to do so by me, and without any leading 



- I'nlrss, as Krcms prolalile, the following extract from Mairan's Trailf Physique d Ilixturirjiie tic I'Aurore Sor&ile, refers to 

 tiin-li u ilifli-roiicc : " J'ai encore observe 1 plusieurs fois, qu'apres que la Lumiere Zodiaeale avait cessi ! de paraitre le soir 

 SOUS sa furiiir .It- lauce ou de fuseau, Unite la partie du coudiuiit demeurait phis iVlaiivi- ijur la rrMr du del, sur 30 ou 40 

 <!' -HM .-, d'amplitude." P. 36. 



