58 



♦ KNO^A^LKDGE ♦ 



[January 2, 1888. 



unlike our terrestrial home, and must have had in the past, 

 as they will have in the future, quite different life histories. 

 But .such is certainly the case. It might be inferred from 

 what we know of the disproportion of the masses, and all 

 the more certainly from what we have recently learned to 

 consider extremely probable respecting their general resem- 

 blance in structure. (For, unlike collections of unlike 

 materials might by some strange chance have like life his- 

 tories ; but such similar Ufe histories could never occur in 

 unlike collections of like materials, or in like collections of 

 unlike materials.) 



It is, however, noteworthy how, even within each family 

 of planets — the family of giant planets and the family of 

 terrestrial planets — differences of size and mass exist which 

 suggest marked differences of life history, and also enable 

 us to infer from analogy great differences among the com- 

 ponent members of higher systems, as sidereal systems, 

 systems of such systems, and so on to higher and higher 

 orders endlessly. I have said that the whole of the inferior 

 family of planets is less in mass than twice our earth ; in 

 other words, our earth surpasses all the rest put together. 

 Venus in turn surpasses Mars, Mercury, and the moon 

 together ; Mars surpasses Mercury and the moon together ; 

 each member of the family, in fine, surpasses all those less 

 than itself taken together. Turning to the f^imily of giant 

 planets, we find the same law there. Jupiter surpasses 

 Saturn, Uranus, and Neptune together some two and a half 

 times ; Saturn surpasses Uranus and Neptune together more 

 than threefold ; Neptune surpasses Uranus and all the 

 rest (moons, rings, cfcc.) of the outer system, with the whole 

 system of terrestrial planets and satellites thrown in. 



{To he co7ifinued.) 



LARGE TELESCOPES. 



HAVE been glad to notice that my friend Pro- 

 fessor Young has come round to the opinion 

 I liave been somewhat strenuously maintaining, 

 that the great telescopes which have lately been 

 made are capable of better and more interest- 

 ing work than hitherto has been accomplished 

 with them. I have not seen yet the article 

 itself in the Forum, wherein Professor Young has indicated 

 the value of great telescopes, and the way in which work 

 done with them can increase our knowledge and extend the 

 horizon of astronomy ; but I have before me a characteristic 

 passage fx'om his essay, the tone of which shows clearly that 

 Professor Young fully indorses the views I have expresed 

 respecting the fine telescopes made so skilfully by the Clarkes 

 and others, and (in several cases) presented so generously to 

 astronomers by men or societies of adequate means. 



" The reasonableness of wanting larger telescopes still," 

 says Professor Young, " is identically the same as that of 

 wanting a telescope at all." This, though somewhat 

 tautologically expressed, is in reality the essence of the 

 whole matter. Astronomy wanted telescopes that moi-e of 

 the universe might be seen and studied, and as far as pos- 

 sible understood ; and each increase of telescopic power has 

 come in lesponse to the longing of astronomy for a wider 

 range of view, increased insight and better understanding of 

 the wonders which lie concealed from ordinary vision in the 

 remote depths of space. 



When one of these far-seeing eyes of astronomy, promising 

 keener vision than had yet been attained, has been provided, 

 and when one of the observing army of astronomy has been 

 set in charge of it, high expectations are naturally formed 

 respecting the work it will accomplish. No one who under- 



stands optical laws can for a moment doubt that such a 

 telescope will do more than one of inferior light-gathering 

 power. This is so, even though a smaller instrument be to 

 some degi-ee superior in actual quality ; but as a matter of 

 fact our opticians are improving year by year the quality of 

 their instruments while increasing the size of the gi-eat eyes 

 they make for scanning star-strewn space. Accordingly 

 astronomy has a right to expect that, even though no actual 

 discoveries may be made by means of a new telescope of 

 superior qualities, the details of objects already known will 

 be better examined, and so be more fuUy understood. 



As Professor Young well says, " It is not possible now to 

 go out at night as some seem to think " — who must be 

 entirely ignorant of the work astronomy has already done — 

 " and pick up discoveries as one would gather flowers in a 

 forest ; but we may be sure of this," the large telescope 

 " will collect data, with micrometer, camera, and spectro- 

 scope, which will remove many old difficulties, will clear up 

 doubts, will actually advance our knowledge— and what is 

 still more important, will prepare the way and hew the 

 steps for still higher climbing towards the stars." The last 

 half sentence may have more metaphor than meaning, more 

 rhetoric than reasoning ; but though we may not quite 

 know how much Professor Young i-eally means by hewing 

 out steps for climbing towards the stars (after all this is 

 not more highfalutin than Horace s " star-striking with his 

 sublime top"), his main argument is sound. A larger 

 telescope, even when used only for going over ground 

 already surveyed with smaller ones, is capable of doing most 

 important and valuable work. The small telescope may dis- 

 cover objects, precisely as the naked eye discovered the sun 

 and moon and planets ; but the larger one will show better 

 what those objects really are, revealing details which before 

 had been either wholly unseen or so imperfectly seen as to 

 be misunderstood. A larger telescope still will show the 

 details of those details, and fresh details, to be still further 

 and more completely analysed when higher powers are 

 applied — if only the larger telescope is zealoTisly applied to 

 such work. 



Many interesting examples might be cited of the way in 

 which large telescopes properly used complete the work 

 begun by smaller ones. 



Consider, for example, the discovery of the sti-ange 

 Saturnian appendage which we now know as the ring 

 system of Saturn. As every one knows, it was Galileo, 

 with his little telescope, who discovered that Saturn had 

 something about him which was unlike anything yet seen. 

 Old Saturn, said Galileo, in his fanciful way, has two 

 satellites which attend him on his way. Later, in a more 

 businesslike communication to Kepler, he said : — " Saturn 

 consists of three stars in contact with one another." And 

 last, addressing the world of science, he announced that he 

 had observed the remotest (or the highest, "as it was still 

 the fashion to call the most distant) planet, to be triform — 

 altissimum planetam tergiminum observari. Such was the 

 discovery of the Saturnian ring-system. No larger telescope 

 could rediscover it ; but every increase of telescopic power 

 applied to Saturn has taught us something more about the 

 system. Galileo was never able to understand why the 

 attendants who guided Saturn on his way were so variable 

 in aspect, and still less why, when he looked at Saturn in 

 1612, he could see no attendants at all. Hevelius, with 

 larger instruments went some way, but not very far, towards 

 interpreting the mystery. He analysed as well as he could 

 the Saturnian changes, and this is his sesquipedalian report 

 of the results he obtained: "Saturn," said he, "presents 

 three various figures to the observer — to wit, in manner 

 following: — first, the monospherical ; secondly, the tri- 

 spherical ; thirdly, the spherico-ansated ; fourthly, the ellip- 



