"Then it must be something like surveying?"
"Yes; the same principles are applied. Here is a sketch, which shows the earth A, and B is the equatorial line. C is the position of the sun on September 20, or on June 20."
"Why are they in the same position on both days?"
"Yes; the sun crosses the equator September 20,[p. 213] on its way south, and then it again recrosses the equator coming north six months afterwards. On either of those days, if a person should stand at D, and look at the sun, there would be a line E, which projects out from the earth to the sun, and that is called the equatorial line."
"It is exactly at right angles to F, which passes through the poles. Now the drawing shows two other positions, namely G and H. These represent the extreme points of the travel of the sun north and south, or the positions that the sun occupy on Dec. 20, and June 20 of each year."
"I see," said Harry. "The points G and H are just 23 degrees north and south of the equator."
"That is correct, and there is another thing which can be learned from their positions."
"I know what it is."
"What?"