188 FRAGMENTS OP SCIENCE. 



that the drainage of nearly half a continent is com- 

 pressed into this space, the impetuosity of the river's 

 rush may be imagined. . Had it not been for Mr. Bier- 

 stadt, 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. Yast 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, 

 carrying away the lighter drops, and leaving the 

 heavier ones behind. Wafted in the proper direction, 

 rainbows appeared and disappeared fitfully in the light- 

 er mist. In other directions the common gleam of the 

 sunshine from the waves and their shattered crests was 

 exquisitely 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 



