IN DESCRIPTIVE ASTRONOMY. 113 



16. In what part of the heavens do we see the new 

 moon ? The old moon ? The crescent moon ? 



(See Astronomy, p. 127 et seq.) 



It is a very interesting experiment to notice how soon after 

 conjunction we can observe the new moon. Observers have de- 

 tected her when twenty-three hours old, and an instance is on 

 record of the moon's thin crescent being seen early one morn- 

 ing before sunrise, and after sundown the following day. 



17. What is the Golden Number in the almanac? 



(See Astronomy, p. 145.) 



18. Why do we have more lunar than solar eclipses ? 



(Soc Astronomy, p. 146.) 



Really, solar eclipses occur more frequently than lunar eclipses, 

 but the latter are . of tener seen at any particular place, because 

 they are visible over a larger area of territory on the earth. 



19. In ivhat direction do the horns of the moon turn ? 



(See Astronomy, p. 127.) 



20. Is the " tidal wave " a progressive movement of 



the ivater ? 



(See Astronomy, note, p. 148.) 



The wind raises the particles of water, and gravity draws 

 them back again. They thus vibrate up and down, but do not 

 advance. The forward movement of the wave is an illusion. 

 The form of the wave progresses, but not the water of which 

 it is composed, any more than the thread of the screw which 

 we turn in our hand, or the undulations of a rope or carpet 

 which is shaken, or the stalks of grain which bend in billows 

 as the wind sweeps over them. Near the shore the oscillations 

 are shorter, and the waves, unbalanced by the deep water, are 

 forced forward till the lower part of each one is checked by the 

 friction on the sandy beach, the front becomes well-nigh ver- 

 tical, and the upper part curls over and falls beyond. 



21. Why does the sun "cross the line" in some years 

 on March 21, and, in others, on March 22 ? 



(See Astronomy, p. 99.) 



Leap-year also throws the dates back one day. 



