CHAPTER V 



THE SKY SUNSETS CLOUDS THUNDERSTORMS 



THE SKY. In addition to simple observations on meteorology 

 the attention should be directed at an early date to the apparent 

 movements of the sun, to the alternation of day and night, to 

 the rhythm of the seasons, and to the correlated phenomena. 



If, as has been suggested, the more striking points in regard 

 to the atmosphere are studied during school excursions, it will 

 be natural at the same time to direct attention to the great 

 vault of the sky. To country children this great vault is of 

 course familiar from the first, but the attention of town-bred 

 children should be specially directed to it. They should be 

 made to notice that whenever we have a clear view the horizon 

 is circular, and that where a portion only is visible this forms 

 a part of a circle. If the ascent of a hill forms one school ex- 

 cursion, as from many centres it may conveniently do, emphasise 

 especially the fact that our view increases in extent as we ascend, 

 the horizon always keeping its circular form. Take advantage 

 of short halts for rests to take special note of the approximate 

 rise since the last halt, and simultaneously of the extent to which 

 the view has increased. Make the class note roughly, by the aid 

 of the Ordnance map, which should always be carried on the 

 excursions, the approximate range of the view in miles at differ- 

 ent points. This is a very important matter, and one which is 

 too much neglected. For the teacher's benefit it may be noted 

 that the distance to which the view should theoretically extend, 

 allowing for the rotundity of the earth, can be readily calculated. 

 The accompanying diagram illustrates the principle of the cal- 

 culation. Let a semi-circle be drawn to represent a section of 

 the earth. Let A and B represent points on a mountain on the 

 surface. Lines drawn from these points to touch the surface 

 of the semi-circle define the limits of the horizon in the two cases, 



