Page:Astronomy for Everybody.djvu/156

This page has been validated.
132
THE SUN, EARTH, AND MOON

the waters out into the form of an ellipsoid, and when it once gives them the motion necessary to keep this form, that motion keeps up after the moon has passed the meridian, just as a stone continues to rise after it has left the hand or a wave goes forward by the momentum of the water. The other cause is found in the interruption of the motion by the great continents. The tidal wave, as it is called, meeting a continent, spreads out in one direction or the other, according to the lay of the land, and may be a long time in passing from one point to another. Thus arise all sorts of irregularities in the tides when we compare those in different places.

The sun produces a tide as well as the moon, but a smaller one. At the times of new and full moon the two bodies unite their forces and cause the highest and lowest tides. These are familiar to all dwellers on the seacoast and are called spring tides. About the time of the first and last quarters the attraction of the sun opposes that of the moon and the tides do not rise so high or fall so low, and these are called neap tides.

This article is issued from Wikisource. The text is available under Creative Commons Attribution-Share Alike 4.0 unless otherwise noted. Additional terms may apply for the media files.