e sun,
but the effect is precisely the same as it would be if the sun moved,
and, accordingly, I use that language. Now how long does it take the sun
to pass round the earth?"

"Twenty-four hours."

"Does he go toward the west or toward the east from us?"

"Toward the west."

But it is not necessary to give the replies; the questions alone will be
sufficient. The reader will observe that they inevitably lead the pupil,
by short and simple steps, to a clear understanding of the point to be
explained.

"Will the sun go toward or from the Rocky Mountains after leaving us?"

"How long did you say it takes the sun to go round the globe and come to
us again?"

"How long to go half round?" "Quarter round?"

"How long will it take him to go to the Rocky Mountains?"

No answer.

"You can not tell. It would depend upon the distance. Suppose, then, the
Rocky Mountains were half round the globe, how long would it take the
sun to go to them?" "Suppose they were quarter round?"

"The whole distance is divided into portions called degrees--360 in all.
How many will the sun pass in going half round?" "In going quarter
round?"

"Ninety degrees, then, make one quarter of the circumference of the
globe. This, you have already said, will take six hours. In one hour,
then, how many degrees will the sun pass over?"

Perhaps no answer. If so, the teacher will subdivide the question on the
principle we are explaining, so as to make the steps such that the
pupils _can_ take them.

"How many degrees will the sun pass over in three hours?"

"Forty-five."

"How large a part of that, then, will he pass in one hour?"

"One third of it."

"And what is one third of forty-five?"

The boys would readily answer fifteen, and the teacher would then dwell
for a moment on the general truth thus deduced, that the sun, in passing
round the earth, passes over fifteen degrees every hour.

"Suppose, then, it takes the sun one hour to go from us to the River
Mississippi, how many degrees west of us would the river be?"

Having thus familiarized the pupils to the fact that the motion of the
sun is a proper measure of the difference of longitude between two
places, the teacher must dismiss the subject for a day, and when the
next opportunity of bringing it forward occurs, he would, perhaps, take
up the subject of the sun's motion as a measure _of time._

"Is the sun ever exactly over our heads?"

"Is he ever exactly south of us?"

"W