33 



been suggested), stands the fact, that the luminosity of the 

 satellites compare about equally with that of the planet. We 

 can hardly imagine these comparatively small bodies to retain 

 any sensible amount of their supposed original incandescence. 

 They may, however, receive a considerable amount of light 

 from the planet itself. This question is one of great interest, 

 and should be investigated, as it probably will be, on a more 

 accurate and scientific basis. 



"IS JUPITER SELF-LUMINOUS?" 

 Bx A. B. Biggs. 



It is with some diffidence that I submit the following paper, 

 partly because I am doubtful of its being a subject of 

 general interest, and partly from a consciousness that the 

 experiments in the eourse of my investigation of the subject 

 did not attain the degree of accuracy which I had hoped for. 

 Perhaps, however, the fact that the question which I set 

 myself to solve is intimately connected with that of the 

 physical condition of Jupiter, and inferentially also of all 

 the giant planets may lend an interest to the subject. 



In the concluding part of my paper on the occultation of 

 Jupiter in April last (read 8th June), I referred to the 

 question of Jupiter's intrinsic brilliancy, and expressed the 

 hope that the question would be scientifically investigated. 

 In order to clear the way, I will first state the case. Jupiter is, 

 roughly speaking, about five times the earth's distance from 

 the sun. It is impossible, therefore, that he can receive from 

 that luminary more than -} s (one twenty-fifth) part of the 

 intensity of illumination which reaches the earth ; that is, in 

 inverse proportion to the squares of the distances. Now, from 

 the time of my first telescopic acquaintance with Jupiter, I was 

 struck with the impression that his brightness far exceeds 

 what, by the above rule, it ought to be. The question 

 naturally arises, how is this want of accordance with the 

 laws of radiation to be accounted for, presuming it to exist ? 

 Some modern astronomical works just refer to this question, 

 but as a rule they pass it over lightly. 



Chamber's Astromony devotes but one short paragraph to- 

 the question, from which I quote as follows: — "Bond com- 

 puted that Jupiter actually emits more light than it 

 receives (!) ; but whether we accept this problematical result, 

 or the more trustworthy one obtained by Zolncr, strong 

 indications of inherent luminosity in Jupiter seem to exist ;. 

 and this points to the conclusion that this planet is itself a 

 miniature Sun." Professor Newcomb says : — " A still more 

 remarkable resemblance to the sun has sometimes been 



C 





