224 Proceedings of the Royal Irish Academy. 



Date.— 1^15, Mareli 31^ 8\ 

 . Place of Ohservation. Off Cape St. Yincent. 



Form. — The Zodiacal Light was well seen. The upper part ap- 

 peared to intersect a line passing through a and /3 Greminorum, aboiit 8° 

 or 10° south of the latter star. On this occasion the southern boundary 

 of the lumiaous haze was much more definite than the northern. 

 There was an evident nucleus or brighter region included by the 

 outer haze. This nucleus was about 25° in length, and almost in- 

 Tolved the Pleiades on its northern side. (See Diagram 5.) 



SUMMAET. 



The observations detailed in this memoir appear to indicate : — ■ 



(1.) That the Zodiacal Light is emitted by matter partly liquid and 

 partly solid, intermixed with gas. 



(2.) That it reaches, and probably suiTounds the earth, as shown 

 by the visibility of the spectrum when viewing any part of the sky un- 

 occupied by the Milky "Way, and by the change of form seen when the 

 observer passed from S. to N. latitudes. (Shown in the Diagrams.) 



It only remains for me now to exj)ress my deep sense of the honour 

 which the Academy have conferred upon me by committing their instru- 

 ment to me for this work ; as well as my regret that other avocations, 

 while abroad and in charge of a very different species of research, 

 together with innumerable circumstances connected with the instru- 

 ment, the weather, the presence of the moon and even of Venus before 

 inferior conjunctions, have rendered this Eeport much less complete 

 than it would otherwise have been. 



