28 THE WORLD MACHINE 



flashing, whirling planets for just such a machine, and, ignorant 

 of Kepler's laws, backing little Mars for a winner against big 

 Jupiter or the earth ! Surely a marvellous flight of the imagina- 

 tion, thus to reduce the whole solar system to the workings of a 

 wheel, not of chance but of fate ; and yet that is what the 

 mighty intellect of Archimedes achieved. His planetarium, so 

 admiringly and accurately described by Cicero, 1 was mistaken 

 only in placing the earth at the centre. Its construction was 

 the feat of an intellectual giant whose mental level has been 

 attained but rarely in the history of the race. 



Thirty times distant from the sun as the earth, and so faint 

 among the crowd of stars that its character as a " wanderer " 

 was not detected until sixty years ago, the planet Neptune 

 lies at the outer rim of this solar wheel. The expanse of its 

 orbit is unthinkably vast ; the earth, 90 millions of miles from 

 the sun ; Neptune thirty times 90 millions. Already the earth 

 has been lost in immensity ; viewed from the sun it would 

 appear scarcely larger than does Mercury to us at its brightest, 

 and far surpassed by Venus or Mars ; viewed from Neptune 

 it would be invisible to the naked eye, as Neptune is to us. 



But the human mind, having reached such heights and 

 depths, will not leave off. What lies beyond ? In what un- 

 imaginable abyss of space is fixed the crystal sphere of the stars ? 

 The objection urged by Tycho against the ideas of Coppernicus 

 was that if the earth spins about the sun, the fixed stars would 

 appear to occupy a different position according as they were 

 viewed from one side of the sun or the other say, at the 

 spring and autumn equinoctials. There would be a certain 

 displacement ; they would have an appreciable " parallax." 

 And Tycho, observing genius as he was, could find none. 



But what Tycho, and Galileo as well, thus vainly sought 

 has been found. Marvellous instruments, devised since their 

 day, have detected the parallax of a considerable number of 

 stars, and we know now that the distance of the farthest planet 

 is to that of the nearest star as an hour to a year. The flight 

 of light from the sun to Neptune, speeding at 186 thousands of 

 miles per second, requires four hours, to the earth eight minutes, 

 to the nearest star four and a half years. Try to comprehend 

 it who can ! The moon is distant from us by ten circumferences 

 1 De Republica, Book I. 



