"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?"
"When he is exactly south of us, or, in other words, exactly opposite to us in his course round the earth, he is said to be in our meridian; for the word meridian means a line drawn exactly north or south from any place."
There is no limit to the simplicity which may be imparted, even to the most difficult subjects, by subdividing the steps. This point, for instance, the meaning of meridian, may be the subject, if it were necessary, of many questions, which would render it simple to the youngest child. The teacher may point to the various articles in the room, or buildings, or other objects without, and ask if they are or are not in his meridian. But to proceed:
"When the sun is exactly opposite to us, in the south, at the highest point to which he rises, what o'clock is it?"
"When the sun is exactly opposite to us, can he be opposite to the Rocky Mountains?"
"Does he get opposite to the Rocky Mountains before or after he is opposite to us?"
"When he is opposite to the Rocky Mountains, what o'clock is it there?"