ASTRONOMY. 179 



American Academy of Arts and Sciences contains a very valuable paper 

 by Mr. .1. Sea'-le on Ibe zodiacal ligbt, in wbich be bas collected and 

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

 cii)al observers of the zodiacal ligbt. The points taken up are tbe ap- 

 proximate position of the zodiacal cone in tbe visible bemispbere of tbe 

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

 southern boundaries at successive elongations ^KP apart. Tbe details 

 of more than G50 observations by Jones, Ileis, Schmidt, and others are 

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

 [)lete]y summarized in a number of other tables showing the monthly 

 means, &nd means for difl'erent series. 



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

 place of the light sliould be referred rather to the corresponding (changes 

 in the place of tbe ecliptic in tbe visible bemisphere than to the geo- 

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

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

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

 pheric absorption bas the importance here assigned to it, in tbe study 

 of tbe zodiacal ligbt, we cannot expect to determine tbe true position of 

 the ligbt on any occasion by tbe simple methods beiet^ofore in use.'> 

 Direct i)hotometric observations must be made, or, failing these, ob- 

 servers "must compare together different i)ortions of the ligbt 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 tbe vague information now before us with regard to 'zo- 

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

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

 well as its apparent changes from hour to hour." 



In dealing with this question of tbe photometric observation of tbe 

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

 Sir W. Herschel's observations tbe Milky Way would appear tobe about 

 two magnitudes brighter than the mean brightness of the skj". On this 

 estimate the biigbter parts of the zodiacal ligbt would be commonly 

 three or four magnitudes brighter than tbe surrounding sky. 



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

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

 ligbt; I have merely to remark witb regard to tbe ordinary meteoric 

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

 aginary meteoric bodies or rings witb whicb it bas usually been con- 

 nected and retain merely the conce^>tion of meteoric dust diffused 

 throughout the solar system. Jt may be shown uuitbematically, if we 

 regard tbe meteoric particles as solids reHectiug light irregularly, that 

 an appearance like the zodiacal cone witb an indefinite vertex would 

 result." [The Observatory, September, IbSi, page 205.) 



