Burton — Note on the Zodiacal Light. 219 



5680 and 4610+ expressed in seventh-metres ; the units employed by 

 Professor Angstrom in preparing his maps of the Solar Spectrum, and 

 adopted in tliis notice. Eepeated impressions of the existence of a 

 narro-^ bright band, situated at, or very near to, the less refrangible 

 end of the continuous spectrum were received this evening, and the 

 wave length of the bright band determined to be 5680. Strong suspi- 

 cions were entertained that there was a darkish band to which the 

 wave length 5360 ±10 was assigned, by the measures taken. These 

 suspicions were strengthened by the evidence of another and iadepeu' 

 dent observer. 



Date. — June 11'^, 9^, SO'", local mean time. 



Place of Ohservation. — Twenty miles IN". E. fi'om Grand Canary. 



Spectrum. — ^As on the preceding night, the central region of the 

 Zodiacal Light yielded an almost continuous spectrum, the sensible 

 limits of which had the wave lengths 5670 and 4640 seventh-metres, 

 according to the measures obtained on this occasion, the first quoted 

 being probably the more trustworthy, on account of the much more 

 definite termination of the spectrum at its less than at its more refran- 

 gible end. J^o mention is made of the bright line seen last night, in 

 the notes made on the present occasion, but a suspicion is recorded 

 that another very narrow and extremely faint existed, the refrangibi- 

 lity of which was less than that of the more defined limit of the con- 

 tinuous spectrum. (As June 11 was the only occasion on which the 

 second bright line was even suspected, it is not included in the accom- 

 panying representation of the Zodiacal Light Spectnim, the details of 

 which are laid down fi'om the mean of the measures obtained, con- 

 verted into wave lengths by curves of interpolation). (Diagram 1.) 



The continuous spectrum was almost interrupted by a well-marked 

 darkish streak, to which was assigned the wave length 5379. 



Folarhation. — A Savart arrangement yielded traces of polarization 

 in planes sensibly parallel to the principal axis of the Light. These 

 traces of polarization could hardly be due to lingering twilight, the 

 depression of the sun below the horizon being not far from 35° at the 

 time of observation. (Diagram 1.) 



Bate. — June 12'', 9^ to \1^, 10^, local mean time. 



Place of Ohservation.— Lai. 24^° I^. Long. 16° W. 



Spectrum. — The Zodiacal Light appeared much brighter than on 

 June ll"", and the lowest power of the specti'oscope was employed. 

 The spectrum was shai-ply terminated on the less refrangible side, and 

 I was convinced that there was in this position a well-defined band, 

 brighter than any other part of the spectrum, the breadth of which 

 was estimated to be approximately ec^ual to that of Frannhofer's group 

 (b), as seen with the same instrument. The wave length of the bright 

 band was determined to be 5680. The dark streak seen last night was 

 again detected, and its position recorded by two observers indepen- 



