Professor Airy, in his _Six Lectures on Astronomy_, gives a masterly
analysis of a problem of considerable intricacy, viz. the determination
of the parallax of the sun, and consequently of his distance, by
observations of the transit of Venus, the connecting link between
measures upon the earth’s surface and the dimensions of our system.
The further step of investigating the parallax, and consequently the
distance of the fixed stars (where that is practicable), is also
elucidated; and the author, with evident satisfaction, thus sums up the
several steps:
By means of a yard-measure, a base-line in a survey was measured;
from this, by the triangulations and computations of a survey,
an arc of meridian on the earth was measured; from this, with
proper observations with the zenith sector, the surveys being also
repeated on different parts of the earth, the earth’s form and
dimensions were ascertained; from these, and a previous independent
knowledge of the proportions of the distances of the earth and
other planets from the sun, with observations of the transit of
Venus, the sun’s distance is determined; and from this, with
observations leading to the parallax of the stars, the distance
of the stars is determined. And _every step in the process can be
distinctly referred to its basis, that is, the yard-measure_.