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fleets an Atlantic roller as easily as a ripple produced 

 by a sea bird's wing ; and in the presence of large re- 

 flecting surfaces the existing differences of magnitude 

 among the waves of ether may disappear. But suppos- 

 ing the reflecting particles, instead of being very large, 

 to be very small, in comparison with the size of the 

 waves. In this case, instead of the whole wave being 

 fronted and in great part thrown back, a small portion 

 only is shivered off. The great mass of the wave passes 

 over such a particle without reflection. Scatter then, a 

 handful of such minute foreign particles in our atmos- 

 phere, and set imagination to watch their action upon 

 the solar waves. Waves of all sizes impinge upon the 

 particles, and you see at every collision a portion of the 

 impinging wave struck off by reflection. All the waves 

 of the spectrum, from the extreme red to the extreme 

 violet, are thus acted upon. But in what proportions 

 will the waves be scattered ? A clear picture will enable 

 us to anticipate the experimental answer. Remember- 

 ing that the red waves are to the blue much in the rela- 

 tion of billows to ripples, let us consider whether those 

 extremely small particles are competent to scatter all 

 the waves in the same proportion. If they be not and 

 a little reflection will make it clear to you that they are 

 not the production of color must be an incident of the 

 scattering. Largeness is a thing of relation ; and the 

 smaller the wave the greater is the relative size of any 

 particle on which the wave impinges, and the greater 

 also the ratio of the reflected portion to the total wave. 

 A pebble placed in the way of the ring-ripples pro- 

 duced by our heavy rain-drops on a tranquil pond will 

 throw back a large fraction of the ripple incident upon 

 it, while the fractional part of a larger wave thrown back 



