THE APPARENT MOVEMENTS OF THE SUN 67 



to consider these facts in their human relations. Further, by 

 contrasting London with our own locality, or if London be the 

 home locality with another town, such as Edinburgh or Aberdeen, 

 we have shown that the winter days get shorter and the summer 

 days longer as we go nearer and nearer the Pole. We have illus- 

 trated this so far as possible by pictures and stories of the Arctic 

 day and of the Arctic night. 



We have travelled, in imagination, from London to the Far 

 North, and we have seen that as we go north the difference in 

 length between day and night becomes greater both in summer 

 and winter. Suppose we reverse our journey. Now we find that 

 the disproportion in length between the two diminishes as we go 

 southward, until at London the longest day is about i6| hours, 

 and the longest night about i6J- hours. Suppose in imagination 

 we prolonged our journey still further south, we should find that 

 the disproportion went on diminishing until at last the longest day 

 and the longest night were each (about) 12 hours long, that is, until 

 the days and nights were always of the same length. This point is, 

 of course, the Equator, and once it is passed the disproportion 

 recommences until we arrive again at the Polar night and Polar 

 day of the Antarctic region. If we begin, as has been suggested 

 above, with some of the differences which the variations in length 

 of night and day make in our daily life, then it is comparatively 

 an easy matter to make clear the special conditions which prevail 

 in a region where night and day are always of approximately equal 

 length. 



In the above summary treatment we have taken no note of 

 twilight, and have regarded the length of day as the period between 

 sunrise and sunset. This is of course incorrect, for the daylight 

 lingers after the sun's rim has dipped beneath the horizon, giving 

 us a longer or shorter period of twilight. Legally, as all bicyclists 

 know, in this country daylight is regarded as lasting for one hour 

 after sunset, and as beginning one hour before sunrise. This law 

 holds everywhere from north to south, though it is of course only 

 an approximation to the actual conditions. It is a very useful 

 exercise, whenever this is possible, to make the pupils mark the 

 actual onset of darkness, as tested by the power to read print 

 in the open, or to see objects across the road, or in some similar 



