THE MOON'S PHASES. 



517 



At A 



It is 



a direct line. The phases, c and G, are the moon's "quadratures." 

 we see the sun shining on the moon, but we only have the dark side, 

 then " new " moon ; but by degrees, as she goes 

 round in her orbit, we perceive a small crescent- 

 shaped portion, lighted up by the sun at B and 

 /;. At c we have the first quarter or half-moon. 

 When she is in opposition she is at full moon, and 

 so on to the last quarter and conjunction again. 



The moon's phases may be easily shown by 

 means of a medium-sized lamp to represent the 

 earth, a smaller one to serve as moon, and a light 

 to act as sun all at the same height. Colour the 

 41 lunar " globe white, and if we move it about 

 the " earth " globe, we shall see the various phases 

 of the moon in the sharp shadows. 



THE TIDES. F 'g- 568. Crescent Moon. 



The ebb and flow of our tidal waters depend upon the moon to a great 



extent. The phenomenon is so common, that we need only refer to it, but 



the cause of the tides may be stated. Twice every day we have the tides twelve 



hours apart, and the flow and ebb are 

 merely examples of the attraction of gravi- 

 tation, which is exercised upon all bodies, 

 either liquid or solid. The tides are highest 

 at the equator and lowest at the poles, 

 because the tropics are more exposed to 

 Fig. 5 6 9 .-Moon-s attraction. fa Q influence of the lunar attraction. 



By the small diagram (fig. 569) we shall be able to see in a moment how 



the moon acts. The moon being nearer to the earth at b, the water will be 



naturally attracted to the ball, ;;/, and cause high water (a] ; and a similar 



effect will be produced opposite, because the 



earth is attracted, so the waves are higher 



than the ground which has been attracted 



away from the water, and the waters will flow 



in and cause a high tide at d, but not so high 



a tide as at the opposite point, a. It can 



then be understood that there will be low 



water at the other two sides, e and f, 



because the water has been taken away, so 



to speak, for the high tides at a and d. We 



shall learn more of this under Physical 



Geography. 



n i t . i * t Fig. 570. New Moon. 



The moon revolves round the earth in 



a changeable elliptical orbit, intersecting the ecliptic at certain points ca//ed 

 Nodes. When the moon is nearest to the Earth she is said to be in perigee 



