CHAPTER XXV 



HERSCHEL AND THE HELTER-SKELTER FLIGHT 

 OF THE STARS 



THE surface velocity of the earth, especially between the tropics, 

 is high seventeen miles per minute, fifty times swifter than 

 the swiftest cannon-ball. Seen from the centre of the earth, 

 it would appear very slow ; the hands of a clock turn twenty- 

 four times while the earth turns once. Relatively, a huge Ferris 

 wheel, revolving once in a few minutes, goes hundreds of times 

 as fast. The whole great earth booms through space at nearly 

 sixty times the speed of its surface in revolution, nineteen miles 

 per second, two thousand times the cannon-ball. Yet from the 

 sun, this dizzy flight would be imperceptible save to repeated 

 observation ; the earth would pass over only one degree of a 

 circle in a day. We could think of it as fixed at the end 

 of a spoke in a wheel ; the earth turns about this solar axis once 

 in a year. 



For us the crystal sphere of the stars is a globe, our earth its 

 centre. Does it too revolve ? Should we ever know if it did ? 



When measurements of the telescope had reached an accuracy 

 of a second of arc and the stars revealed no parallax, it was 

 clear they were beyond two hundred thousand times the distance 

 of the sun. Conceive that they are all turning about our sun, 

 like the planets. The length, the circumference, of circles are 

 to each other as their radii. If the stars moved as swiftly as 

 the earth, then at this distance their " year " would be two 

 hundred thousand of ours. They would require six hundred 

 of our years to cover a degree. Their apparent annual motion 

 then would be about six seconds of arc. 



No such motion as this could be perceived ; for a long time 

 no motion at all. Yet, here and there, it did seem that, in 

 very long periods, some of the stars had shifted place slightly. 



Early in the century Halley, the sower of much seed, the 



harvest from which others would reap, had pointed out that 



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