Science, Geology and Physics 



various sizes, decreasing in the lower part, until they were lost 1877 

 in the general mist which surrounded the lower part of the Falls. BarJow 



The continual recurrence of these jets, and the continual recur- 

 rence of the jarring action above referred to, point to the con- 

 clusion that both effects are due to one cause, and my object in 

 drawing attention to the subject is to endeavor to suggest the 

 nature of the cause which is producing these effects. 



Proceeding to a nearer view of the waters by going beneath 

 the Falls, and looking at and through them, it becomes apparent 

 that the water which flows over the upper rocks in a continuous 

 curved stream, breaks up into masses of greater or less magnitude 

 during its descent, so that air in large quantities gets in and 

 between the falling masses of water. In this intermixing of air 

 and water it may frequently happen that a quantity of air is 

 surrounded and enclosed in a heavy mass of water, and falling 

 in this state with a velocity due to the height of 1 50 ft. or 1 60 

 ft., the contained air would become suddenly and violently 

 compressed on striking the rocks below. The energy of the 

 charge of compressed air thus suddenly generated, would burst 

 through the thinnest layer of its surrounding water, and so con- 

 stitute a species of explosion, carrying a portion of the water with 

 it. Assuming the weight of water which generated the com- 

 pression to be greater than that on which the energy of the com- 

 pressed air operated, the effect would be to project the smaller 

 mass of water with a greater velocity than that due to the 

 original fall. The supposition most consistent with the observed 

 phenomena appears, therefore, to be that the two effects, namely, 

 the jets of water and the jarring action shown on the doors and 

 windows, are both due to the explosions or sudden expansions of 

 air compressed by the falling water as above described. There 

 are several circumstances which appear to favor this supposition. 



1 . The sudden upward blasts of air accompanied by water, 

 felt by persons when beneath the Falls, which are probably only 

 minor effects of a like action. 



2. The jarring motion imparted to the doors and windows 



571 



