THE MOON 169 



Provide a rod about four feet long, sharpened at one end, 

 so that it may be thrust into the ground (a tripod is more con- 

 venient, but more difficult to make). 



To the upper end attach a platform of board about four inches 

 square, on which to place a level, by means of which the plat- 

 lorm is to be made horizontal. A small iron spirit level can be 

 pbtained for fifteen cents. 



On the edge of the platform is tacked a thick cardboard with 

 a semicircle drawn on its outer side. The diameter of the circle 

 lies on a level with the surface of the platform. The semicircle 

 jis marked off in degrees as carefully as possible, and marked 

 from o degrees to 180 degrees, the 90th degree being on the end of 

 the radius exactly perpendicular to the surface of the platform. 

 With this apparatus, using pins as sights, the position in degrees 

 of the moon above the horizon may be read for a few successive 

 evenings at the same hour. See if the rate of movement, thus 

 determined, corresponds to the rate calculated by the obser- 

 vation of how many days the moon takes to make a revolution 

 (360 degrees). 



Another line of questioning to be pursued is that in 

 relation to the cause of the changing of the illuminated part. 

 Pupils may, in their own way, prepare models to illustrate this. 



Why is one side of the moon always turned toward the earth? 

 How long is the moon's day? 



Children from ten to twelve years of age have worked out 

 all the above with no trouble except the setting of the work. 

 This work, of course, must be given out for the pupils to do at 

 liome of evenings but if the teacher can meet them, some even- 

 ings, much more interest might be aroused. A small telescope, 

 or even a good spy glass, will add greatly to the interest. 



After the above work, the pupil can more successfully under- 

 stand the motions of the earth. 



