This phenomenon is the progressive motion of the centre of gravity of
the whole solar system in universal space. Its velocity, according
to Bessel, is probably four millions of miles daily, in a _relative_
velocity to that of 61 Cygni of at least 3,336,000 miles, or more than
double the velocity of the revolution of the earth in her orbit round
the sun. This change of the entire solar system would remain unknown
to us, if the admirable exactness of our astronomical instruments of
measurement, and the advancement recently made in the art of observing,
did not cause our progress towards remote stars to be perceptible,
like an approximation to the objects of a distant shore in apparent
motion. The proper motion of the star 61 Cygni, for instance, is so
considerable, that it has amounted to a whole degree in the course of
700 years.--_Humboldt’s Cosmos_, vol. i.