34 PROCEEDINGS OP SECTION A. 



plasticity were such that axial rotation was putting a great strain 

 on its cohesion. There is one remarkable feature the result of 

 recent observations of this body, namely, that the orbits of the 

 satellites appear to be in a plane coincident with the bulging, 

 but that bands apparently equatorial are seen to exist in a plane 

 differing from that of the satellites by over 40 degrees. 



The spectrum of this planet shows the presence of free hydrogen 

 on its surface, from which we may conclude its present condition 

 is more nearly the solar one than any member of the group, 

 except, perhaps, Neptune, whose spectrum appears very analogous 

 to that of Uranus. We can see very little of Neptune, and do 

 not even yet know its rotation period. This question, as well as 

 that of the existence of other planets outside of him, form 

 problems for the future. 



The spectroscope has helped us to a knowledge of the nature of 

 the fixed stars and nebulae that was formerly little dreamt of. 

 On account of the immense distance of the nearest of these 

 bodies, seen through our largest telescopes, they appear simply as 

 points of light, but analyse this light by the spectroscope and a 

 flood of knowledge comes to the observer. 



Most of the stars show a spectrum of lines, either bright from 

 a glowing gas, or dark from the absorption effects of overlying 

 vapour, in many cases marvellously like our sun. Indubitable 

 evidence is presented to us of the presence of metals, gases, and 

 other substances familiar to us on the earth and in the vapours of 

 the sun, and indeed of their being in all probability suns in them- 

 selves. We find, however, that there are several varieties of 

 spectra among the stars, yet not so numerous but they can be 

 grouped into half a dozen classes or so. One group exhibits a 

 spectrum almost identical in character with the solar one, others 

 exhibit a few bright lines only, some again have both bright and 

 dark lines, many show the fluted spectrum characteristic of 

 certain elements at comparatively low temperatures, while others 

 exhibit a continuous spectrum, or a spectrum partly continuous 

 and partly broken by lines or flutings. The appearances tell us 

 plainly of the existence of matter at high but different 

 temperatures, from that of a Bunsen burner, perhaps up to that 

 of the cauldron of glowing Bessemer steel, and onwards to that of 

 the solar surface itself. The conclusions we have come to with 

 regard to most of the principal fixed stars is that they are bodies 

 very analogous to our sun, and probably consisting of the same 

 matter, but from their different conditions revealing to us the 

 presence only of such elements as are vapourised, or rendered 

 incandescent, at the temperature which is at present maintained 

 on their surface. We account for the occasional sudden increase 

 in the brightness of a star — indeed, all variability of stars — by 

 sudden or gradual alterations of this temperature from causes 

 which cannot, so far, be explained, except upon an hypothesis 



