"This is not at all difficult, and will answer for any kind of an ellipse, short or long, narrow or wide. This is called the "gardener's method." The main thing is to get the two points, E and F. This distance is always half of the long diameter A B, no matter what that may be, and this distance is then transferred by taking C as the starting point, measuring from there until the other point of measurement cuts the long diameter, as at E and F.
"The ellipse has many peculiar and useful qualities, which you will doubtless discover before long."
IX
TIDES
Now, papa!" said Jessie the following evening, after Mr. Gregg and the family had strolled down to the river bank to enjoy the cool air, "you promised to tell me about the tides and the moon—when you could spare time. Haven't you got time now?"
"I may as well say all I intended now, my dear, and leave some other matters for future consideration. As this subject may tax your patience, I hope you, Fred, and George, will give me your earnest attention.
"In order to have a clear understanding of the movements of the tides and their supposed causes, you must know something of the moon's influence over them; as this knowledge will aid you very much in remembering what I am about to say.
"The earth is a globular body. One reason for this belief, among many others, is that sailors or others who go to sea soon observe that as they sail from shore, the lower portions of mountains, steeples or other high objects, are gradually lost sight of while the higher parts do not so soon disappear. Persons on shore first notice the upper portions of masts, and the smoke-stacks of approaching vessels, which would not be the case, if the earth were a plane, but is very easily accounted for, on the supposition of its being a sphere, as you can readily understand by looking at [Fig. 66]. Several navigators have sailed completely round the earth by continuing in the same direction, and coming at last to the same place from which they started. The earth, however, is not a perfect sphere but a spheroid like an orange; having its equatorial longer than its polar diameter or axis. It is flattened at the poles, and more protuberant at the equator. The diameter at the equator is 7,977 miles, and at the poles 7,940, a difference of 37 miles.