and that the estimate must be raised to at
least thirteen million. In 1670 Cassini showed that these numbers were
altogether inconsistent with the facts, and gave as his conclusion
eighty-five million.

The transit of Venus over the face of the sun, June 3, 1769, had been
foreseen, and its great value in the solution of this fundamental
problem in astronomy appreciated. With commendable alacrity various
governments contributed their assistance in making observations, so that
in Europe there were fifty stations, in Asia six, in America seventeen.
It was for this purpose that the English Government dispatched Captain
Cook on his celebrated first voyage. He went to Otaheite. His voyage
was crowned with success. The sun rose without a cloud, and the sky
continued equally clear throughout the day. The transit at Cook's
station lasted from about half-past nine in the morning until about
half-past three in the afternoon, and all the observations were made in
a satisfactory manner.

But, on the discussion of the observations made at the different
stations, it was found that there was not the accordance that could have
been desired--the result varying from eighty-eight to one hundred and
nine million. The celebrated mathematician, Encke, therefore reviewed
them in 1822-'24, and came to the conclusion that the sun's horizontal
parallax, that is, the angle under which the semi-diameter of the earth
is seen from the sun, is 8 576/1000 seconds; this gave as the distance
95,274,000 miles. Subsequently the observations were reconsidered
by Hansen, who gave as their result 91,659,000 miles. Still later,
Leverrier made it 91,759,000. Airy and Stone, by another method, made
it 91,400,000; Stone alone, by a revision of the old observations,
91,730,000; and finally, Foucault and Fizeau, from physical experiments,
determining the velocity of light, and therefore in their nature
altogether differing from transit observations, 91,400,000. Until the
results of the transit of next year (1874) are ascertained, it must
therefore be admitted that the distance of the earth from the sun is
somewhat less than ninety-two million miles.

This distance once determined, the dimensions of the solar system may
be ascertained with ease and precision. It is enough to mention that
the distance of Neptune from the sun, the most remote of the planets at
present known, is about thirty times that of the earth.

By the aid of these numbers we may begin to gain