January 2, 1888.1 



♦ KNOWLEDGE ♦ 



One of the most impressive thoughts respecting the sun's 

 mass is the might which it represents — might ahsolutely 

 essential to his rule over the solar system. To give b^- a 

 simple example an idea of the sun's tremendous power, 

 imagine an immensely powerful magnet acting at a distance 

 of one mile on a particle of uon. and trj' to conceive the 

 slow motion by which at first that particle would respond 

 to the magnetic attraction. Now suppose this magnet ! 

 replaced by a body having the sun's attractive might, but 

 all collected in a one-inch globe ; and suppose, further, that 

 this concentrated sun acts on a body from the distance of a 

 mile all the time (a whole second is all the time I ask for), 

 retreating from the body as, under its attractive influence, 

 the body moves towards it, and so always maintaining that 

 distance of one mile unchanged. Then, in that second, the 

 attraction on the body would be so great as to communicate 

 a velocity of 31,000 millions of miles per second. Or, in a 

 period of time so inconceivably short as one millionth part 

 of a second, our sun's mass, concenti-ated into a one-inch 

 globe, would at a mile distance (kept unchanged) communi- 

 cate the tremendous velocity of 31,600 miles per second. 



Our sun surpasses in mass all the members of his family 

 together more than 74.5 times, so that there is no question 

 of his absolute supremacy over that family. Yet 8ii- John 

 Herschel fell into a mistake when he asserted that, if all 

 the planets were in a row on the same side of the sun, each 

 at its proper mean distance from the sun, the centre of 

 gravity of the whole system would lie far within the globe 

 of the sun. The centre of gravity would be 937,000 miles 

 from the sun's centre. This does not prevent the sun from 

 exerting supreme sway over the planets, however. Indeed, 

 the fixed centre round which the sun and all the planets 

 travel — this centre being the centre of gravity of the solar j 

 system at the moment — is nearly always within a much 

 smaller distance from the sun's centre than I have just 

 named, since it vei-y seldom happens that even three of the 

 chief planets of the system conjoin theii- influence on the 

 same side of the sun. The sun's motion around the common 

 centre may be regarded as made up of motions in a nearly 

 circular ellipse at a mean distance of 460,000 miles due to 

 Jupiter's attraction, in another at a mean distance of 

 253,000 due to Saturn's attraction, and in two others at 

 mean distances of 79,000 and 145,000 miles respectively, due 

 to the attractions of Uranus and Neptune, all other attrac- 

 tions being relatively inappreciable. 



And jast here I cannot but touch, in the way of correc- 



biUions, eight hundred and twelve millions, foar hundred and fifty- 

 six thousand, two hundred and fifty-nine ; the English name for 

 the same number is three hundred and twenty-four trillions, five 

 hundred and sixty-five thousand four hundred and eighty-two 

 billions, seven hundred and ninety-three thousand eight hundred 

 and twelve millions, four hundred and fifty-six thousand two 

 hundred and fifty-nine. Each name contains forty words, but the 

 English, with its hundreds of thousands of trillions, billions, 

 millions, and upits, is much more systematic, and conveys a much 

 clearer idea than the American with its hundreds of quintillions, 

 quadrillions, trillions, billions, millions, thousands (observe the 

 entire change in the character of the nomenclature here), and units. 

 I think it hardly necessary for me, after now some fourteen years, 

 during which 1 have shown the utmost readiness to appreciate 

 things American at iheir full value— a readiness which many among 

 my fellow countrymen regard as extreme and unpatriotic (though 

 that is nonsense) — to explain that it is from no desire to find fault 

 that I thus dwell upon the unscientific and illogical nature of the 

 system of numeration adopted in American schools. The system, 

 employed as it now is, throughout the whole of the great American 

 section of the English-speaking race, involves serious inconvenience 

 from the mere fact that it differs from that employed elsewhere 

 where English is spoken and written. Probably when it was intro- 

 duced American arithmeticians hardly looked forward to the time 

 when America would take so large a share of the scientific work of 

 the English-speaking races as she does at present. 



tion, on the strange mistake made by my friend Mr. Mattieu 

 Williams in imagining that the motion of our sun in the 

 path thus determined, about the common centre of gravity 

 of the solar system, can in any appreciable degree affect the 

 condition of the sun's interior. He has presented in his 

 suggestive book, " The Fuel of the Sun " — a book full of 

 novel ideas, but not free from startling mistakes — the quaint 

 notion that as our sun goes circling round and about the 

 common centre of gra\ity of the solar sy.st€m, his material 

 is swayed about with all sorts of effects and influences, 

 stirring it up, intermingling it, keeping it active, and so 

 forth, as might happen, for example, if the glowing fuel 

 within some great furnace were constantlv stirred up by the 

 swaying round of the whole furnace by some powerful 

 mechanism. The mistake is, perhaps, a not tmnatural one. 

 Something akin to it was made even by so skilful a mathe- 

 matician as Professor .Simon Newcomb, when, in the first 

 edition of his " Popular Astronomy," he presented the tides 

 as a product of centrifugal tendencies called into action as 

 our earth circles around the common centre of gravity of 

 the earth and moon.* 



Mr. Williams's idea about a stirring up and shaking 

 together of the solar fuel is entirely erroneous. If the sun 

 were swinging bodily round a fixed axis, in such sort that 

 while some parts of his mass (being near to that axis) 

 moved much, there would result a certain stirring up of the 

 solar material which might, for anything I know to the con- 

 trary (though I have given no attention to so purely hypo- 

 thetical a case), have some such effects as Mr. WiUiams 

 imagines. But there is no such swinging. The sun moves 

 as a whole (with inconceivably slow motion, too), around or 

 upon his somewhat complex orbit, each particle moving in 

 an orbit of exactly the same size, so that there is no relative 

 motion among the different parts of his mass, and therefore 

 no strains or pressures are produced and no interchanges of 

 position occur. 



I imagine that few recognise fully the next most striking 

 feature of the solar system after the amazing superiority of 

 the sun's mass — I mean the startling discrepiucy between 

 the outer family of planets and the inner. Each contains 

 four primary bodies — .Jupiter, Saturn, Uranus, and Neptune 

 forming one. Mercury, Yenus, the Earth, and Mars forming 

 the other. But while the combined mass of all the four 

 inner planets is not quite twice the mass of the earth, the 

 four outer planets together exceed the earth in mass no less 

 than — in round numbers — 450,000 times. Can we possibly 

 regard two families so disproportioned as resembling each 

 other in kind 1 I have been engaged now so many years in 

 endeavouring to persuade students of astronomy, both on « 

 prion grounds and on the more satisfactory evidence of 

 observed facts, that the giant planets are unlike the terrestrial 

 planets even as they are unlike the sim, each forming a 

 definitely distinct class, that though I may say I have now 

 succeeded, I can hardly expect very readily to persuade the 

 general reader that Jupiter and Saturn must be altogether 



* I was rather interested in this mistake, because on the strength 

 of it, and a kindred mistake about the earth's reeling motion in 

 25,868 years being similarly caused, I had been taken sharply to 

 task by the editors of " Johnson's Cyclopedia " for not introducing 

 some such explanation of the tides and of precession into the 

 astronomy of the " American Cyclopsedia." Here, wrote my severe 

 and anonymous critic (or to this effect), was our American astro- 

 nomer, all ready with a new cut-and-dried explanation of these 

 phenomena, and Messrs. Appleton pay this " blawsted Britisher " for 

 reproducing the old one. The old one, however, chances to be right ; 

 the new one (as it appeared shortly after in the first edition of 

 " Newcomb's Astronomy ") is wholly wrong ; and even in the very 

 mild and modified form in which it appears In the second edition, 

 it has no value whatever as an original explanation, being only a 

 recondite way of presenting the most unsatisfactory portions of the 

 old one. 



