INTRODUCTION. U 



In 1848, Professor G. Piazzi Smyth read before the Royal Society of Edinburgh a valuable 

 paper giving account of observations made by him in South Africa some years previously, and 

 also of an instrument invented by him for getting the position of the apex of the Zodiacal 

 Light. To his paper (published in the Transactions of the Society, vol. xx, part iii) is appended 

 an interesting exhibition of this phenomenon, as seen at the Cape of Good Hope in July, 1845. 



There is only one subject more to be noticed in this history of observations on the Zodiacal 

 Light. At the twenty-second meeting of the British Association for the Advancement of 

 Knowledge (in 1852),- a paper was read from the Kew Observatory, giving account of observa- 

 tions from January to April, 1850, by Mr. H. R. Birt. It has little in detail, and gives a 

 statement, which is of little value, of the changes of inclination of the axis of the Zodiacal 

 Light towards the ecliptic; but there occurs, moreover, the following passage in the records of 

 the earlier part of March: " One evening, there was a sudden brightening of the light for an 

 instant, and also variations in its lustre of an intermittent character. These intermissions of 

 brightness were observed on the same evening by Mr. Lowe, of Nottingham. They are 

 described by the author not to be of the nature of pulsations, in the usual acceptation of the 

 term, but to consist of alternate brightenings and dimniiugs of the entire mass of light, such as 

 might be produced by the approach and recess of a luminous body." (Am. Jour. ScL, xv, 

 new series, page 121.) 



Baron Humboldt also noticed similar appearances, as we learn from the following passage in 

 his published works: "I have occasionally been astonished, in the tropical climates of South 

 America, to observe the variable intensity of the Zodiacal Light. As I passed the nights, 

 during many months, in the open air, on the shores of rivers and on llanos, I enjoyed ample 

 opportunities of carefully examining this phenomenon. When the Zodiacal Light had been 

 most intense, I have observed that it would be perceptibly weakened for a few minutes, until it 

 again suddenly shone forth in full brilliancy," &c. (See Cosmos, vol. i.) 



In our own country, some attention has been paid to the Zodiacal Light by individuals here 

 and there ; and our astronomers have been earnestly desirous of facts, on which to ground 

 opinions ; but without being able themselves to accumulate any extensive data, on account of 

 the high northern aspect of our skies, and the low angle at which the ecliptic ranges with their 

 horizon through much of the year. 



MY OWN OBSERVATIONS AND THEIR RESULTS. 



The historical items just given have been collected from various authorities since my return 

 to the United States ; for, previous to sailing on this cruise, I had given the Zodiacal Light no 

 attention, more than to be aware that there was such a thing ; and I had never seen it to know 

 it as such. 



I hope the reader will now pardon a little egotism in these remarks ; for it is proper that ho 

 should know the circumstances of my observations, and thus be able to form his own opinion 

 about their reliability and the results. While I was busy with preparations for the cruise, my 

 friend, Professor Dana, of Yale College, suggested to me that I would have good opportunities 

 for observations on the Zodiacal Light; but my mind was then fully occupied with other 

 matters, and I could not have found time for resorting to libraries, or for making other prepa- 

 rations, if, indeed, I had known how they were to be made. Fortunately, at my last visit to 

 my old home at the Naval Academy in Annapolis, off which our frigate was then lying, I pro- 



