XVI INTRODUCTION. 



But I consider this as only the commencement of work. We need more facts. Those in 

 this book are very few, compared with what are required in the case. It is my own purpose to 

 make further observations, if possible, for a year or fifteen months, at some one spot, at or near 

 the equator, so as to have comparisons, as the ecliptic passes at equal distances over head in the 

 different portions of the year. And if my life is spared still further, I hope to continue my 

 work to its end. 



But we need many observers. One judgment may make mistakes many of them, where mis- 

 takes can so easily be made. We need many judgments, so that one may correct another ; and 

 especially is it desirable that, for one year at least, there should be a series of simultaneous 

 observations at the equator, and at points remote from it, both at the north and south. This 

 I hope to be now able to effect. 



At this stage of our work, effected and proposed, it may, perhaps, seem to be premature to 

 draw conclusions ; but still there are certain things that seem to force themselves on the mind 

 from the data here afforded ; and, if the conclusions which I shall now proceed to draw are not 

 decisive to the reader's mind, they can at least furnish subjects for discussion that may, in the 

 end, bring us to the truth. 



DEDUCTIONS FROM THESE OBSERVATIONS. 



1- 



It seems to be quite conclusive, on an inspection of these charts, that ive never, at any 

 one time, see the whole actual extent of the Zodiacal Light. This subject can, perhaps, be eluci- 

 dated by noticing a common event, a cloud, silvered at one edge by the rays of the declining 

 sun. The sun may be shining on the bordering, quite around that cloud; and, if so, it is send- 

 ing off, from every portion of the border, an equally brilliant, silvery light. But our eye is in a 

 position to catch this reflection from only one portion of it, and the rest is dull to our vision. 

 If we could with great rapidity change our positions, other portions of the silvered edge would 

 show themselves according to our changes of place. So, also, when a rainbow is presented to 

 our eye : the myriads of drops of falling water in the whole rain-shower are sending off, from 

 each drop, reflections of light in all directions, and the universal atmosphere about us is full 

 of these brilliant, variously-colored rays ; but only that portion which, to us, forms the rain- 

 bow-arch, can reach our eye, and all the rest is lost to our sight. 



So it is also with the Zodiacal Light ; and the proof that we never see the whole of its 

 extent at once, is manifest in the following facts: 



1 . That when I was in a position north of the ecliptic, the main body of the Zodiacal Light 

 was on the northern side of that line. 



2. When I was south of the ecliptic, the main body of the Zodiacal Light was on its southern 

 side. 



3. When my position was near or on the ecliptic, this Light was equally divided by the 

 ecliptic, or nearly so. 



4. When, by the earth's rotation on its axis, I was, during the night, carried rapidly to or 

 from the ecliptic, the change of the apex, and of the direction of the boundary-lines, was 

 equally great, and corresponded to my change of place. 



5. That, as the ecliptic changed its position as respects the horizon, the entire shape of the 

 Zodiacal Light became changed, which would result from new portions of the nebulous matter 



