Suppose that the periodic times in which the earth and
Venus revolved had no simple relation to each other, then the points
of their tracks in which the two planets came into line with the sun
would be found at different parts of the orbits, and consequently the
disturbances would to a great extent neutralise each other, and
produce but little appreciable effect. As, however, Venus and the
earth come back every eight years to nearly the same positions at the
same points of their track, an accumulative effect is produced. For
the disturbance of one planet upon the other will, of course, be
greatest when those two planets are nearest, that is, when they lie
in line with the sun and on the same side of it. Every eight years a
certain part of the orbit of the earth is, therefore, disturbed by
the attraction of Venus with peculiar vigour. The consequence is
that, owing to the numerical relation between the movements of the
planets to which I have referred, disturbing effects become
appreciable which would otherwise be too small to permit of
recognition. Airy proposed to himself to compute the effects which
Venus would have on the movement of the earth in consequence of the
circumstance that eight revolutions of the one planet required almost
the same time as thirteen revolutions of the other.
Pages:
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324