146 PEOCEEDINGS OP THE AMERICAN ACADEMY 



V. 



THE ZODIACAL LIGHT. 



By Arthur Searle. 



Presented October 10, 1883. 



At the outset of any inquh-y into previously neglected phenomena, 

 the observations or experiments which can be made are necessarily 

 somewhat vague. The questions to which we endeavor to obtain 

 replies are drawn up more or less at random, and this is even more 

 true of the hypotheses by which we relieve the monotony of our first 

 observations. A "considerable improvement in the conditions govern- 

 ing our inquiries will be made when we begin to discover the details 

 to which our attention should be directed in order to arrive at the more 

 general knowledge originally desired. But the discovery of these 

 details usually demands a jjatient examination of the confused mass of 

 material first collected by observatiou. It is not so likely to be 

 forwarded by the formation of new hypotheses, although it is undoubt- 

 edly true that a lucky guess may give a fortunate direction to our 

 work, upon which we should have been long in deciding if we de- 

 pended only upon the study of what had already been observed. Still, 

 it is never advisable to neglect this study in the hope that it can be 

 saved by guessing. 



For these reasons, it has seemed to me worth while to collect, and 

 partially to reduce, upon a uniform system, the published work of 

 several observers of the zodiacal light. I have confined my attention 

 for the present to their evening observations, as the morning observa- 

 tions would in any case require separate consideration, and as it has 

 been difficult to find time, under the pressure of other occupations, for 

 even the limited discussion herewith presented. From Serpieri's study 

 of the observations of Jones (to be further mentioned below) we 

 have, moreover, some means of comparing the most important pub- 

 lished series of morning observations with the eveninn: observations of 

 the same observer. 



The data hero collected relate to the approximate position of the 

 zodiacal cone in the visible hemisphere of the sky, to the elongation 



