self. In all other respects it
floats in vacuum, or what is so nearly so as to be thus termed. Now, let
the uninstructed reader imagine a large circular table, with a light on
its surface, and near to its centre. The light shall represent the sun,
the outer edge of the circle of the table the earth's orbit, and its
surface the plane of that orbit. In nature there is no such thing as a
plane at all, the space within the orbit being vacant; but the surface of
the table gives a distinct notion of the general position of the earth as
it travels round the sun. It is scarcely necessary to say that the axis of
the earth is an imaginary line drawn through the planet, from one pole to
the other; the name being derived from the supposition that our daily
revolution is made on this axis.

Now, the first thing that the student is to fix in his mind, in order to
comprehend the phenomenon of the seasons, is the leading fact that the
earth does not change its attitude in space, if we may so express it, when
it changes its position. If the axis were _perpendicular_ to the plane of
the orbit, this circumstance would not affect the temperature, as the
simplest experiment will show. Putting the equator of a globe on the outer
edge of the table, and holding it perfectly _upright_, causing it to turn
on its axis as it passes round the circle, it would be found that the
light from the centre of the table would illumine just one half of the
globe, at all times and in all positions, cutting the two poles. Did this
movement correspond with that of nature, the days and nights would be
always of the same length, and there would be no changes of the seasons,
the warmest weather being nearest to the equator, and the cold increasing
as the poles were approached. No where, however, would the cold be so
intense as it now is, nor would the heat be as great as at present, except
at or quite near to the equator. The first fact would be owing to the
regular return of the sun, once in twenty-four hours; the last to the
oblique manner in which its rays struck this orb, in all places but near
its centre.

But the globe ought not to be made to move around the table with its axis
perpendicular to its surface, or to the "plane of the earth's orbit." In
point of fact, the earth is inclined to this plane, and the globe should
be placed at a corresponding inclination. Let the globe be brought to the
edge of the table, at its south side, and with its upper or north