THE MAKING OF A SUN-DIAL 



27 



Drive a peg into the ground, and to its top attach a little rod so that its end may 

 be turned to any part of the sky. Early in the morning direct the pointer towards 

 the sun (it will properly set when turned so that it casts a shadow no larger than its 

 cross section on a piece of paper held behind it), and record the position of its end 

 by driving a stake into the ground, so that the top of the stake shall just touch the 

 end of the pointer. 



Eepeat the process several times in the day. The tops of the stakes will then 

 make part of a circle whose plane is parallel with that followed by the sun. Lay a 

 piece of cardboard (with one end upon the ground behind the peg) so that it touches 

 the tops of all the stakes. The angle which the card makes with the ground repre- 

 sents the latitude required. * 



At the Tiffin's Boys' School, Kingston-on-Thames, 

 the latitude is taken by means of an upright 

 knitting needle at noon, though in this case " the 

 distance of the sun north of the equator " is ob- 

 tained from the " Nautical Almanac." In figure 

 34 16 '6 cm. is the height of the knitting needle, 

 P. 



9 '9 cm. the length of the shadow which it 

 casts. 



O B the sun's direction. 



O C the direction of the equator. 



The angle Z B is 31. 



20 12' 12" is the distance of the sun north of 

 the equator. 



Then the latitude = 31 + (20 12' 12") = 51 

 12' 12". 



FIGURE 31 . 



Having obtained the proper angle (figure 31) fold down the 

 corner of a stiff piece of paper and draw a line A B, making 

 the required angle with the doubled edge. Mark out other 



* See " Physical Geography," by William Morris Davis and William Henry Snyder. 

 Ginn & Co., 1898 (price 5s. 6d.), page 388. 



