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at those times of the year when the Zodiacal Light cannot be seen in 

 the Nortliein hemisphere ; to test, by means of these new data, — 

 which, besides the novelty of the geographical position, had the fur- 

 ther one of being determined by instrumental measurement, — what 

 laws of the phenomena may be considered to have been satisfactorily 

 made out, and what required further elucidation ; and to recommend 

 these latter to the attention of observers situated in more favourable 

 parts of the world than those commanded by European Observatories 

 generally. 



After discussing the history of the subject, and mentioning the 

 results arrived at by difl'erent observers, the author mentions the 

 manner in which his attention was first particularly directed to the 

 subject, describes the particular course of observation which he then 

 commenced, and which consisted principally in observing the right 

 ascension and declination of the apex of the light, by means of a 

 small equatorial instrument of particular construction, which gave 

 results not affected with more than 2° of probable error. Combin- 

 ing his own observations with those of former investigators, the author 

 concludes, that the hypothesis proposed by Cassini, and subsequently 

 maintained by La Place, Schubert, Poisson, Biot, and Humboldt, viz., 

 that the Zodiacal light is in the form of a ring encircling the sun, is 

 decidedly untenable, but that it is rather, as first suggested by Mairan 

 and since afi&rmed by Olbers and Sir John Herschel, in the form of a 

 lenticular mass. Mairan's idea, too, of the body being excentrically 

 disposed about the sun, being endued with a rotation, and occasionally 

 crossing the earth's orbit, seems to be confirmed. But the exact 

 quantity of such excentricity, the period of rotation, the position of 

 the plane of the body, the question of any actual periodical increase 

 in the size and brightness of the Zodiacal light, and the physical na- 

 ture of that light, whether entirely reflected, or whether, as rendered 

 probable by some observations, partly direct, are matters, for the sa- 

 tisfactory determination of which more data are required. For the 

 assistance of those who may be inclined to prosecute the inquiry, 

 the author adds descriptions, both verbal and pictorial, of what the 

 Zodiacal light is like, what observers may expect to see ; and men- 

 tions the times of the year at which, in difl'erent latitudes, the phe- 

 nomenon may bo best seen, together with a number of other atten- 

 dant circumstances which arc necessary to be complied with, in order 

 to procure undeniable observations. 



VOL. II. P 



