ASTRONOMY. 179 



American Academy of Arts and Sciences contains a very valuable paper 

 by JMr. A. Se;uie on the zodiacal light, in which he has collected and 

 reduced on a uniform system the evening observations of the prin- 

 cipal observers of the zodiacal light. The points taken up are the ap- 

 proximate position of the zodiacal cone in the visible hemisphere of the 

 sky, the elongation of the vertex, and the latitudes of the northern and 

 southern boundaries at successive elongations 30° ai)art. The details 

 of more than GoO observations by Jones, Ileis, Schmidt, and others are 

 exhibited in tabular form, whilst their results are conveniently and com- 

 pletel^" summarized in a number of other tables showing the monthly 

 means, and means for different series. 



Mr. Searle supports Jones's view that the apparent changes in the 

 place of the light should be referred rather to the corresponding changes 

 in the place of the ecliptic in the visible hemisphere than to the geo- 

 graphical position of the observer in latitude, and regards it as probable 

 that atmospheric absorption is an important and, perhaps, the only 

 cause of the variations of the zodiacal light in latitude. But " if atmos- 

 pheric absorption has the importance here assigned to it, in the study 

 of the zodiacal light, we cannot exi^ect to determine the true position of 

 the light on any occasion by the simple methods heretofore in use.'' 

 Direct photometric observations must be made, or, failing these, ob- 

 servers "must compare together different portions of the light and also 

 specified portions of the light and of the Milky Way." And the Milky 

 Way must itself be studied in a similar systematic manner. A careful 

 photometric inquiry " is indispensable if we are to substitute definite 

 knowledge for the vague information now before us with regard to ' zo- 

 diacal bands,' the singular phenomenon of the 'Gegeuschein,' and the 

 possibly periodic variations in the main body of the zodiacal light, as 

 well as its apparent changes from hour to hour." 



In dealing with this question of the photometric observation of the 

 light, Mr. Searle mentions the interesting fact that from Celoria's and 

 Sir W. Herschel's observations the Milky Way would appear to be about 

 two magnitudes brighter than the mean brightness of the sky. On this 

 istimate the brighter parts of the zodiacal light would be commonly 

 three or four magnitudes brighter than the surrounding sky. 



Mr. Searle remarks in conclusion : " It is not my intention, on this 

 occasion, to discuss the probability of any explanation of the zodiacal 

 light; I have merely to remark with regard to tlie ordinary meteoric 

 theory, that it gains greatly in simplicity if we dispense with all the im- 

 aginary meteoric- bodies or rings with which it has usually been con- 

 nected and retain merely the conception of meteoric dust diffused 

 througliout the solar system. It may be shown matliematicall.v, if we 

 regard the meteoric particles as solids reflecting light irregularly, that 

 an nppearance like the zodiacal cone with an indefinite veitex would 

 result." {The Observatory, September, lti84, page 265.) 



