I 







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4 



G Jones on the Zodiacal Light. 379 



strongest light -of tlie luminous arcli. The lines aaaa^ aaaa, 

 show its boundaries : the line hhh^ the boundary of the very dim 

 light seen occasionally while I was at my farthest remove from 

 the ecliptic on its southern side; The diagram A on the chart is 

 intended to show the comparative intensity of the light across 

 the Luminous Arch: this intensity being according to the dis- 

 tance of the line ddd from ee. At B is another diagram in 

 which the intensity is shown when the offset noticed above was 



seen ; 



/// 



brightness of the several parts. As to the actual brightness of 

 this Luminous Arch, the following notes from my journal of 

 observations may be satisfactory to the reader. 



Oct. 1i\ 1856. 0^ 20»». "The Luminous Arch at m* has the brightness 

 of the Milky Way at n n,^^ [My zenith was 2° from the Hne cc] 



Oct. 29th, at 9 30. "I compared the briglitness of the Luminous Arch 

 with the Milky Way and thought that at o it was fully as bright as the 

 latter at ppp (quite a bright part of the galaxy) perhaps even at r.'^ 

 [The ecliptic was vertical — the sky remarkably fine for observations.] 



Dec. 2d. 11^ 30"^. "Compared the light with that of the Milky Way, 

 and thought that the part s of the Luminous Arch was equal in bright- 

 ness to that of the Milky Way at 5'." [The night remarkably fine ; my 

 zenith 24° S. of cc] ^ 



Dec. 2Gth, 7^ lO"^. "I thought the light of the Luminous Arch at s 

 was equal to that of the Milky Way at tt^ which is a tolerably bright 

 part of the galaxy." [Sky fine for observations : my zenith 6° S, of ccc] 



Dec. 2'7th, 0^ 45"^. *' The brightness at uau I thought equal to that of 



Wav 



28° S. of ccc.l 



I 



Feb. 3d, 185Y, 4^ 45^. "I thought the Luminous Arch. at icw equal to 

 that of the Milky Way at x : not quite so bright as at y." 



Feb. 4th, 3^ 20"^. "I thought the light of the Luminous Arch from w 

 to 2 was equal to that of the Milky Way at y. [My zenith 1"" S. of 



ccc] 

 Feb. 18th, 10^ 45"^. *' Thought the light at m^ was equal to that of the 



Galaxy at n' : at m^ it was equal to that at w^." 

 Feb. 24th, 9^ 20"'. "The light along the central part of the Luminous 



Arch from m^ to m* was equal to that of the Milky Way at n^ n* :" 



[my zenith 24° S. of ccc] 



The Luminous Arch usually remained -visible in the zenith and 

 the western part of the sky some time (occasionally 15 minutes) 

 afler dawn had decidedly come at the eastern horizon. 



I had also observations of other very interesting phenomena 

 in the heavens and the atmosphere: but, though they are akin 

 to this topic, I do not consider it best to introduce them here. 



The data which we now possess on the Zodiacal Light, seem 

 to lead inevitably to the following conclusions- 



Z 1. That this light is from a great nebulous ring. If there were 

 no interruption from the moon or from clouds, this Luminous 



* See the accompanying star-chart 



