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.