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?"