56 



^ KNOW^LEDGE ♦ 



[January 2, 1888. 



maud acceptance, being based on experiments of a decisive 

 character. Tliey also correspond with theoretical con- 

 siderations, and I expected, indeed, when I inserted Mr. 

 Faith's interesting and suggestive paper, to find his state- 

 ments corrected to some such degree. For it was manifest 

 to me, viewing the matter merely as a problem in hydro- 

 dynamics, that putting a ship's rudder over to either side 

 must tend to cause (apart from loss of way) rotation around 

 a vertical axis passing nearly through the centre of gravity. 

 But I cannot agree with Mr. Robinson that Mr. Faith's 

 deductions become erroneous. On the contrary, Mr. 

 Robinson has proved for us that Mr. Faith's main deduc- 

 tion is sound. If two ships are proceeding on such a course 

 as would bring one slantingly into the side of the other, and 

 they are already close, following the sailing instructions will 

 only make the collision more destructive, unless when the 

 rudder is put over by the latter she pivots round her stern — • 

 which does not happen. Running directly counter to the 

 printed instructions, would, on the contrary, give her a good 

 chance of escape. — Ed.] 



MATERIAL OF THE UNIVERSE. 



HAVE just completed a chapter of a book on 

 astronomy, in which I have had to consider 

 the measuring and weighing of the solar 

 .system, and I must confess that although I 

 have long been acquainted with the v.arious 

 facts in detail which I have found occasion to 

 discuss in the chapter, I have risen from the 

 study of those facts as thus collected with such feelings of 

 awe at the marvels of our universe, .and wonder at man's 

 resolution in mastering tlie secrets of Nature as I have 

 never before experienced — at least in like degree. 



I propose now to run through some of the results belong- 

 ing to tliis chapter in the history of astronomy, and then to 

 .show .something of their bearing on our estimate of the 

 universe, regarded alike with reference to its extension in 

 space and to its duration in time. 



Our earth's weight, not estimated by the comparatively 

 rough methods of compaiison in which a mountain serves 

 as the counter weight, or the approach towards the e.arth's 

 centre permitted in a mine is trusted in to indicate the 

 earth's density, but definitely weighed against known oiasses 

 of matter, amounts to about .590,0.54,000,000,000,000,000 

 tons — a mass easily expres.sed in numbers, l)ut utterly incon- 

 ceivable by the human mind. The moon, at a distance of 

 238,830 miles, has a mass equal to about one eighty-first 

 part of the earth's ; but even her smaller mass is as hopelessly 

 beyond our powers of conception as that of the great globe 

 on which we live. I am not sure but that, looking on the 

 moon as she rides high above tlie horizon and noting how 

 small she looks, queen though she be of the orbs of night, 

 there is not somet hing more i mpressi ve in the thought that that 

 calmly beautiful globs contains 7,300,000,000,000,000,000 

 tons of such matter as makes the mass of our earth, than 

 even in the consideration that our earth weighs nearly 

 eighty-one times as much. The earth had always seemed 

 the very emblem of stability and massive might, insomuch 

 that though man in his days of ignorance imagined compara- 

 tively narrow limits to his terrestrial domain, there were 

 hardly any limits to the mass or quantity of matter he 

 might attribute to her. But the full size of the moon is 

 visible to every human eye ; and the contrast between the 

 apparent and the real is much greater when, for example, 

 we consider that that silvery surface at which we look 

 yonder is 2,160 miles in diameter and contains 7,300,000 



square miles of just such rock surface as we have on our 

 earth, than when, looking out upon our earth as far as the 

 eye can reach, we learn that the real extent of the earth is 

 many thousandfold greater than the area thus .^.urveyed. 

 And if this is so in striking degree in regard to the moon's 

 apparent size, it is still so in more impressive manner when 

 we consider her mass. 



Passing beyond the moon to the region of space outside, 

 we may turn at once to the sun. Within his fiery globe 

 lies very nearly the whole mass of the solar system. He 

 looks no larger than the moon, but he is 60,000,000 of times 

 larger, and more than 26,750,000 of times as massive. His 

 mass surpasses our earth's 330,500 times, a disproportion 

 of wdiose full meaning we can only form a fair idea by con- 

 sidering separately first the inconceivably large mass of the 

 earth, and then the enormous number represented by the 

 figures 330,500. On this last point I may remark that few 

 (so far as my observation has gone) form definite concep- 

 tions of the meaning of large numbers, even when such 

 meaning is well within their power of appreciation. 



To most men 300,000 is a number whicli, even when it 

 represents money, is not definitely difl'erentiated in the mind 

 from such numbers as 200,000 or 400,000, or even from 

 such numbers as 30,000 or 3,000,000. Yet there are simple 

 ways of obtaining a clear idea of what it represents. Draw 

 a straight line 10 inches long, and, completing a square on 

 it, divide up this square into 100 small squares by lines 

 1 inch apart drawn parallel to the sides. Take a corner 

 square, and, dividing its .sides into tenths of an inch, divide 

 it like the large one into 100 small .squares. Then the 

 meaning of the number 10,000 is very clearly shown so soon 

 as we notice that our 10-inch square contains 10,000 such 

 .squares as make up the 1-inch corner square. The eye sees 

 in this case the degree in which 10,000 surpasses 1 ; and we 

 all know the truth of old Horace's saying, Segnius irritant 

 animos demissa per aures, quam qiur sunt oculis suhjecta 

 fidelihus. It is now ea.sy, without further drawing, to imagine 

 ten such squai'cs as our large one, and thus to recognise the 

 significance of the number 100,000. Thirty such squares 

 would picture the meaning of 300,000, the small tenth-of- 

 an-inch square in the corner being the unit. And thus we 

 can readily form a good mental conception of the degree in 

 which the sun's mighty mass surpasses the earth's — though 

 we still remain, and must for ever remain, unable to appre- 

 ciate the stupendous significance of the six hundred millions 

 of millions of millions* or so of tons contained within the 

 bulk of our terrestrial home. 



* According to our English system we call this six hundred 

 trillions. In America the expression would be quintillions. I 

 object altogether to use an expression which has no true significance. 

 It includes the number .5 (quint) ; but no 5 is logically includible in 

 it. A quintillion, according to the English system of numeration, 

 signifies a million raised to the fifth power; according to the 

 American (want of) sjstem, it signifies a million multiplied by a 

 thousand raised to the fourth power. One c.in get a 5 in, indeed, 

 thus : A quintillion is a thousand multiplied by a thousand raised to 

 the fifth power; but that is an obviously unsymmetrioal way of 

 representing a thousand raised to the sixth power. If the American 

 system were sound logically and mathematiciilly, it would not be 

 so convenient as the English system, for when we get into such 

 numbers .as trillions, qu.adrillions, and so forth, which only happens 

 when we are comparing numbers all of whicli are very large, it is 

 desirable not to contuse comjiarison by having too many different 

 names, or (which is the same thing) by separating our classes of 

 numbers by divisions too closely set. Lastly, in giving names to 

 large numbers the English .system is superior to the American, 

 though there is no difference in the numbers of words employed. 

 The first example, taken at random, will serve to show this to the 

 logical arithmetician. Letthe number be 321, 563,482,793,81 2,4,')6,259: 

 for this the American name would be three hundred and twenty- 

 four quintillions, five hundred and sixty-five quadrillions, four 

 hundred and eighty- two trillions, seven hundred and ninety-three 



