rve as an example. I
will suppose that the teacher of a common school undertakes to show his
boys, who, we will suppose, are acquainted with nothing but elementary
arithmetic, how longitude is determined by means of the eclipses of
Jupiter's satellites; not a very simple question, but still one which,
like all others, may be, merely by the power of the subdivision alluded
to, easily explained. I will suppose that the subject has come up at a
general exercise; perhaps the question was asked in writing by one of
the older boys. I will present the explanation chiefly in the form of
question and answer, that it may be seen that the steps are so short
that the boys may take them themselves.

"Which way," asks the teacher, "are the Rocky Mountains from us?"

"West," answer two or three of the boys.

In such cases as this, it is very desirable that the answers should be
general, so that throughout the school there should be a spirited
interest in the questions and replies. This will never be the case if a
small number of the boys only take part in the answers, and many
teachers complain that when they try this experiment they can seldom
induce many of the pupils to take a part.

The reason ordinarily is that they say that _any_ of the boys may answer
instead of that _all_ of them may. The boys do not get the idea that it
is wished that a universal reply should come from all parts of the room,
in which every one's voice should be heard. If the answers were feeble
in the instance we are supposing, the teacher would perhaps say,

"I only heard one or two answers; do not more of you know where the
Rocky Mountains are? Will you all think and answer together? Which way
are they from us?"

"West," answer a large number of boys.

"You do not answer fully enough yet; I do not think more than forty
answered, and there are about sixty here. I should like to have _every
one in the room_ answer, and all precisely together."

He then repeats the question, and obtains a full response. A similar
effort will always succeed.

"Now does the sun, in going round the earth, pass over the Rocky
Mountains, or over us, first?"

To this question the teacher hears a confused answer. Some do not
reply; some say, "Over the Rocky Mountains;" others, "Over us;" and
others still, "The sun does not move at all."

"It is true that the sun, strictly speaking, does not move; the earth
turns round, presenting the various countries in succession to th