DAY AND NIGHT THE SEASONS 



angle between it and the ground is the altitude of the sun, i.e. 

 its height above the horizon. This angle may be measured 

 with a protractor, or, more simply, the height of the stick, the 

 length of the lath, and the distance between the end of the lath 

 and the foot of the stick may all be measured. These measure- 

 ments give the three sides of the triangle, and the children may 

 be shown how to construct a similar triangle to scale, and then 

 measure the angle between the hypotenuse and the base, i.e. 

 the altitude of the sun. 



At the same time explain to the class that this is the principle 

 of the gnomen, which was extensively used by the ancients as 

 a method of obtaining the altitude of the sun and stars. 

 If the members of the class have an elementary acquaint- 

 ance with mathematics, they can of course be shown that the 

 sloping lath is not essential to obtain the altitude of the sun, 

 for the tangent of the desired angle can be obtained by the 



stick perpendicular 



ratio - : , the equivalent of the of an ordinary 



shadow 



horizontal 



SUMMER SOUSTICC 



right-angled triangle. The angle can then be obtained from this 

 tangent by the aid of a book of logarithms. 



By means of the ZE N JTH 

 sloping lath, or by 

 calculation, the noon 

 altitude of the sun 

 should be obtained 

 roughly for a series 

 of dates throughout 

 the year. In spring, 

 weekly observations 

 may well be made, 

 so that the class can 

 follow the upward 

 creep of the sun in 

 the sky, noting at 

 the same time the 

 rise of temperature as the days become longer and the rays less 

 oblique. They should not be told about the solstice until their 



FIG. 6. The noon altitude of the sun at London at the 

 equinoxes and solstices. Compare with Fig. 2. 



