II. 



The Apparent Position of the Zodiacal Liglit. 

 By AETHUE SEAELE. 



Presented October 14, 1SS5. 



In all the explanations of the zodiacal light which have at present any claim 

 to serious consideration, it is assumed that the light is due to finely divided 

 matter of some kind, illuminated either by direct sunlight or by the result of 

 electrical or chemical action. This matter may be only a portion of the atmos- 

 phere, or of some cosmical mass more or less homogeneous. But in this case 

 the illumination is presumed to be confined within certain limits. The object, 

 therefore, which observers of the zodiacal light have ordinarily proposed to them- 

 selves has been the discovery of the position and extent of the matter thus 

 illuminated. Its apparent position in the sky was accordingly first to be deter- 

 mined at particular times, and large numbers of sketches, representing its visible 

 limits, have been made for this purpose, especially within the last fifty years. 



In a previous communication^ I have attempted to derive, from the pub- 

 lished work of the chief observers of the zodiacal light, some conclusions likely 

 to be of service in planning future observations, rather than in determining the 

 apparent position of the zodiacal light from those already made. The prominent 

 result to be obtained from the comparison of sketches of the zodiacal light had 

 always been an uncertainty whether the outlines depicted by the observers 

 afforded any distinct information with regard to the real object to be observed. 

 As is remarked by Schmidt,^ all the observations accumulated in the twelve 

 years preceding 1868 seemed to add nothing to our knowledge with i-egard to 

 the constitution and position of the zodiacal light. On this account, Schmidt 

 recommends closer attention to the fiiint light sometimes seen in opposition to 

 the Sun, and apparently due to causes of the same kind with those by which the 

 zodiacal light itself is produced. 



1 Proc. Am. Acad. XIX. 146. " Astronomische Nachrichten, LXXII. 342. 



