STUDIES IN NATURE 



stance in which light travels cannot be air, for 

 light passes from the sun to the earth through 

 regions far beyond the reach of our atmosphere, 

 which is indeed but a film over the face of the 

 globe. Hence we believe that space is filled 

 with something about which we still know very 

 little, except that it can transmit waves, which 

 if they are very short affect our eyes as light, 

 and if they are very long can affect electrical 

 instruments, and be used in wireless telegraphy. 

 This something is now generally called ' ether.' 

 The best way to begin our study of waves 

 is to watch those that are visible, such as the 

 waves that cross the surface of the sea, or any 

 other sheet of water. If we watch a little piece 

 of floating wood, or a boat, which is lying out at 

 rest, we shall see that the particles of water do 

 not move it forwards, they only move it about 

 near its original position ; it rises and falls as 

 the waves pass. True waves are pulsations or 

 throbbings in the ocean, they seem to beat time, 

 they do not in the end move the water either on- 

 wards or backwards. The waves of the ocean 

 are not all of the same size ; there is not always 

 the same distance between the top or crest of one 

 wave and the crest of the next. The waves of 

 sound too are of different lengths, the short 

 quick ones which strike our ears many times a 

 second produce high, shrill sounds, while the 

 longer waves, fewer of which arrive during a 

 second of time, give low deep tones. In the 



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