SOME NOTES ON JUPITER DURINa HIS OPPOSITION OP 1876. 95 



exhalations from molten matter constituting the body of the 

 planet. But there is sometimes a strange persistency in these 

 features, which seems incompatible with a vaporous nature only ; 

 and I think that those who have had the best opportunities for 

 observation in this particular subject will be the last to hazard an. 

 opinion as to their origin. Unfortunately, too, the spectroscope 

 fails to help us here : for Jupiter, shining as he does by reflected 

 light, gives back the solar spectrum, with the addition of a few 

 lines somewhat similar to those added when the sun is low down, 

 and, consequently, shining through a considerable extent of our 

 atmosphere. The spectrum, too, of Jupiter is, contrary to what 

 many would suppose, exceedingly faint, being only about equal 

 to that of a third magnitude star ; the brilliant aspect that he 

 presents to the eye being occasioned by the immense size of his 

 disk, and not by its intrinsic luminosity. "When I say that 

 Jupiter shines only by reflected light I am aware that amongst 

 some eminent authorities it is believed that he does emit somewhat 

 more light than he receives ; and Proctor, writing on this subject, 

 says — " If Jupiter does not shine somewhat by native light, his 

 surface must possess reflective powers nearly equal to white paper, 

 which is scarcely credible." But this excess of brilliance, if it 

 does exist, is too small to make any difference in the spectrum. 



I feel the limits that I can fairly allow myself for occupying 

 your attention will not permit of my entering into half of the 

 many features which this interesting planet has presented during 

 the present opposition, and of which I am persuaded much is new, 

 and has in consequence never been recorded before. I will not, 

 therefore, dwell now on the phenomena connected with the 

 satellites, their transits, their shadows, and many other details of 

 which more than enough remain for another discussion. Still less 

 would I detain you by any attempt of my own to theorize on these 

 wonderful and complex operations taking place on such a mighty 

 scale — a scale of which the inhabitants of our little globe, 8,000 

 miles in diameter, can form no adequate idea. What, for instance, 

 should we think if we saw, supposing that we could see, a black 

 mass of vapour, or it may be of some far more solid substance, 

 22,000 miles in extent, suddenly break up and disappear in the 

 course of a few minutes ; and yet this very phenomenon was 

 recorded by Sir James South to have taken place on one occasion 

 when he was observing Jupiter. 



There is, however, one theory of Proctor's in reference to the 

 condition of Jupiter as afl'ecting his colour which I will men- 

 tion, as it seems to me to be one of the most reasonable yet 

 broached, and moreover appears to accord well with observation. 

 He thinks at a first view that nothing could appear more sur- 

 prising than a change afl'ecting the colour of a zone-shaped region 

 whose surface is many times greater than the surface of our earth. 



