the planet gradually moved off the sun, the circular edge of the planet
extending out into the darkness was seen to be bounded by a circular arc
of light, and Dr. Copeland, who observed this transit in very favourable
circumstances, was actually able to follow the planet until it had
passed entirely away from the sun, at which time the globe, though
itself invisible, was distinctly marked by the girdle of light by which
it was surrounded. This luminous circle is inexplicable save by the
supposition that the globe of Venus is surrounded by an atmospheric
shell in the same way as the earth.

It may be asked, what is the advantage of devoting so much time and
labour to a celestial phenomenon like the transit of Venus which has so
little bearing on practical affairs? What does it matter whether the sun
be 95,000,000 miles off, or whether it be only 93,000,000, or any other
distance? We must admit at once that the enquiry has but a slender
bearing on matters of practical utility. No doubt a fanciful person
might contend that to compute our nautical almanacs with perfect
accuracy we require a precise knowledge of the distance of the sun. Our
vast commerce depends on skilful navigation, and one factor necessary
for success is the reliability of the "Nautical Almanac." The increased
perfection of the almanac must therefore bear some relation to increased
perfection in navigation. Now, as good authorities tell us that in
running for a harbour on a tempestuous night, or in other critical
emergencies, even a yard of sea-room is often of great consequence, so
it may conceivably happen that to the infinitesimal influence of the
transit of Venus on the "Nautical Almanac" is due the safety of a
gallant vessel.

But the time, the labour, and the money expended in observing the
transit of Venus are really to be defended on quite different grounds.
We see in it a fruitful source of information. It tells us the distance
of the sun, which is the foundation of all the great measurements of the
universe. It gratifies the intellectual curiosity of man by a view of
the true dimensions of the majestic solar system, in which the earth is
seen to play a dignified, though still subordinate, part; and it leads
us to a conception of the stupendous scale on which the universe is
constructed.

It is not possible for us, with a due regard to the limits of this
volume, to protract any longer our discussion of the transit of Venus.
When we begin to s