240 FRAGMENTS OF SCIENCE. 



this space, the impetuosity of the river's rush may be 

 imagined. Had it not been for Mr. Bierstadt, the 

 distinguished photographer of Niagara, I should have 

 quitted the place without seeing these rapids ; for 

 this, and for his agreeable company to the spot, I have 

 to thank him. From the edge of the cliff above the 

 rapids, we descended, a little, I confess, to a climber's 

 disgust, in an ' elevator,' because the effects are best 

 seen from the water level. 



Two kinds of motion are here obviously active, a 

 motion of translation and a motion of undulation the 

 race of the river through its gorge, and the great waves 

 generated by its collision with, and rebound from, the 

 obstacles in its way. In the middle of the river the 

 rush and tossing are most violent ; at all events, the 

 impetuous force of the individual waves is here most 

 strikingly displayed. Vast pyramidal heaps leap inces- 

 santly from the river, some of them with such energy 

 as to jerk their summits into the air, where they hang 

 momentarily suspended in crowds of liquid spherules. 

 The sun shone for a few minutes. At times the wind, 

 coming up the river, searched and sifted the spray, carry- 

 ing away the lighter drops, and leaving the heavier ones 

 behind. Wafted in the proper direction, rainbows 

 appeared and disappeared fitfully in the lighter mist. 

 In other directions the common gleam of the sunshine 

 from the waves and their shattered crests was exqui- 

 sitely beautiful. The complexity of the action was still 

 further illustrated by the fact, that in some cases, as if 

 by the exercise of a local explosive force, the drops were 

 shot radially from a particular centre, forming around 

 it a kind of halo. 



The first impression, and, indeed, the current ex- 

 planation of these rapids is, that the central bed of 

 the river is cumbered with large boulders, aiad that the 



