CHAPTER VII 

 DAY AND NIGHT. THE SEASONS 



WHEN a considerable number of shadow observations have 

 been made, and the most elementary points in regard to the 

 apparent movements of the sun thus made clear, we want to go 

 a few steps farther. The Nature Study course should give at 

 least a generalised idea of the two movements of the earth, the 

 movement of rotation and the movement of revolution, though 

 we want, of course, to treat these subjects much more simply than 

 in a geography course. 



After we have marked one noon shadow, we want to show 

 that, in a period of (about) twenty-four hours, the shadow falls 

 again in the same position, showing that the earth has taken 

 twenty-four hours to return to the position from which it started. 

 Similarly, we want to show that if we mark the shortest shadow 

 at one summer solstice, in about a year from that time the shadow 

 falls again in the same place, showing that the earth has taken a 

 year to return to the point from which we started. In the Nature 

 Study course, however, it would seem that these facts should 

 be considered rather from the point of view of measures of time, 

 that is, of their practical importance, than from the astronomical 

 standpoint. 



Day by day we see the sun cross the sky from east to west. We 

 can easily find the time when he is highest in the heavens by the 

 fact that the shadow of a stick is then shortest. We call this time 

 noon, and it takes (roughly) twenty-four hours for the series of 

 movements whose result is to bring the sun apparently back to 

 the same place. Here, then, is a convenient measure of time. 

 Let us suppose that we are shipwrecked mariners cast upon a 

 desert island. We have no watches, but we must have some 

 way of dividing our days, and therefore we proceed to construct 

 a shadow-clock, a sundial. In some such way we might lead 



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