70 THE BOOK OF NATURE STUDY 



shadows change with the change from morning till evening, so 

 they also change in position with the change from spring to 

 summer and from autumn to winter. Try to find in the school 

 buildings some striking examples to illustrate these changes, for 

 instance, a wall which receives no sun in the winter months. Let 

 the last appearance of the sun here in autumn be carefully marked 

 with the date and hour, and let the class watch in spring for the 

 first illumination by its rays. They will almost certainly be 

 greatly interested in such observations, and they are laying the 

 foundations for a fuller treatment of the sun's movements after- 

 wards. Add to these observations notes upon the position of the 

 sun in relation to landmarks in the vicinity. In the morning on 

 such and such a date it is beside the church, in the evening it 

 sinks behind such a hill, and so on. In this fashion we may obtain 

 general notions of its apparent double movements, the diurnal 

 and the annual. 



Again, by repeating the shadow observations at different 

 seasons, we may easily deduce the fact that the noonday shadow 

 is shortest in summer and longest in winter that it changes 

 throughout the year as it changes in length when watched for a 

 day. We note also that when the shadows grow long in the evening 

 the sun's rays are much less bright we can look at the setting 

 sun without discomfort, while at midday he is too brilliant for 

 us to attempt this. In the same way when the shadows grow 

 long in winter it is a paler, feebler sun than that which casts the 

 short shadow of summer. 



Two little points of practical interest may perhaps be mentioned here. The 

 first is that children should never, under any circumstances, be encouraged or 

 permitted to look directly at the sun, either with the naked eye or with any 

 instrument involving the use of a telescope (i.e. a sextant), unless the eye be 

 protected in some way. While making observations of short duration a piece of 

 smoked glass (or dark bottle glass) held between the eye and the sun is a good 

 protection ; other more effective means are blue " goggles," or, when the telescope 

 is used, the insertion of special smoked or coloured glasses. The point is one of 

 great practical importance, and the difficulty of insisting upon it in each individual 

 case with a considerable 'class must always make shadow observations preferable 

 when dealing with children to any which render direct observation of the sun 

 necessary. 



The second point, which is of importance if more or less continuous shadow 

 observations are to be made throughout the year, is to remember the great length 



