7 8 



THE BOOK OF NATURE STUDY 



FIG. 4. 



line, which can be done with a measuring tape or ruler. A line 

 drawn from D, the point of bisection, to the base of the stick 



is a true north and south line, 

 and marks also the position of the 

 shortest shadow. If the school is in 

 the longitude of Greenwich, then D 

 will coincide^with the point at which 

 the school clock showed noon. If 

 the school is west of Greenwich, 



&L then the point D will be after the 



point marked as coinciding with 

 clock noon. By making the shadow 

 observations at regular intervals of, 

 say, ten minutes, it is possible to cal- 

 culate roughly from them how much 

 apparent noon is after clock noon. 

 This experiment, though more laborious, is more satisfactory 

 than that of trying to find local apparent noon by noting the 

 point when the shadow is shortest, for it will be found in practice 

 that it is not easy to determine the exact moment when the 

 shadow is shortest. 



The north and south line so obtained should be marked 

 permanently, to be used later in geography lessons. The results 

 obtained in this way should be compared with those obtained 

 by the rough rule that, if the hour hand of a watch is made to 

 point to the sun, the direction south lies half-way between the 

 hour hand and twelve o'clock. The accuracy of the line should 

 also be tested by means of the compass, allowance being made 

 for magnetic declination. 



It may be necessary to repeat the experiment on several 

 successive days in order to obtain fair accuracy, and it should 

 be noted that it is always prudent for the teacher to carry out 

 experiments of this kind alone beforehand, as various trifling 

 difficulties present themselves in practice which require care 

 in overcoming. 



If the experiment has been performed on one of the days 

 specified, the stick, chalk line, etc., should be left in position, 

 and the observations repeated the next day. It will be found 



