ng the correct image of the shape is to
imagine how the earth would appear as seen from the moon. In its full
condition the moon is apt to appear as a disk. When it is new, and
also when in its waning stages it is visible in the daytime, the
spherical form is very apparent. Imagining himself on the surface of
the moon, the student can well perceive how the earth would appear as
a vast body in the heavens; its eight thousand miles of diameter,
about four times that of the satellite, would give an area sixteen
times the size which the moon presents to us. On this scale the
continents and oceans would appear very much more plain than do the
relatively slight irregularities on the lunar surface.

With the terrestrial globe in hand, the student can readily construct
an image which will represent, at least in outline, the appearance
which the sphere he inhabits would present when seen from a distance
of about a quarter of a million miles away. The continent of
Europe-Asia would of itself appear larger than all the lunar surface
which is visible to us. Every continent and all the greater islands
would be clearly indicated. The snow covering which in the winter of
the northern hemisphere wraps so much of the land would be seen to
come and go in the changes of the seasons; even the permanent ice
about either pole, and the greater regions of glaciers, such as those
of the Alps and the Himalayas, would appear as brilliant patches of
white amid fields of darker hue. Even the changes in the aspect of the
vegetation which at one season clothes the wide land with a green
mantle, and at another assumes the dun hue of winter, would be, to the
unaided eye, very distinct. It is probable that all the greater rivers
would be traceable as lines of light across the relatively dark
surface of the continents. By such exercises of the constructive
imagination--indeed, in no other way--the student can acquire the
habit of considering the earth as a vast whole. From time to time as
he studies the earth from near by he should endeavour to assemble the
phenomena in the general way which we have indicated.

The reader has doubtless already learned that the earth is a slightly
flattened sphere, having an average diameter of about eight thousand
miles, the average section at the equator being about twenty-six miles
greater than that from pole to pole. In a body of such large
proportions this difference in measurement appears not important; it
is, how