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.