200 . report— 1877. 



Secondly. On looking at the Falls themselves, and especially at the Horseshoe 

 Fall, there appeared from time to time, through the mist which always envelopes 

 the lower part of the Falls, jets of water projected suddenly upwards. These jets 

 frequently rose much ahove the level of the upper part of the Fall. Judging from the 

 known height of the Falls, they frequently rose front 10 to HO feet ahove the upper 

 level. They occurred at varying intervals ; but very few minutes elapsed without 

 seeing one of greater or less magnitude. 



It was also observable that they had a characteristic form, somewhat resembling 

 a pine-tree — that is to say, small or pointed at the top, and widening out 

 downwards. 



They were not formed of a compact mass of water, but had that appearance, 

 which is seen in large fountains, of being composed of lumps of water of various 

 sizes, decreasing in the lower part, until they were lost in the general mist which 

 surrounded the lower part ot the Falls. 



The continual recurrence of these jets, and the continual recurrence of the jarring 

 action above referred to, point to the conclusion that both effects are due to one 

 cause ; and my object in drawing attention to the subject is to endeavour 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 150 or 1G0 feet, 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 constitute a species of 

 explosion carrying a portion of the water with it. 



Assuming the weight of the water which generated the compression to be greater 

 than that on which the energy of the compressed air operated, the effect would be 

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

 original force. 



The supposition most consistent with the observed phenomena appears, therefore, 

 to he 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 b} r the falling water as above described. 



There are several circumstances which appear to favour this supposition : — 



First. 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. 



Secondly. The jarring motion imparted to the doors and windows appears to 

 have no corresponding effect in the solid ground ; from which it may be inferred 

 that the effect is due to concussions conveyed through the air, and not "to the tremor 

 of the earth by the weight of the falling water. 



Thirdly. The characteristic form of the jets, which is similar to that produced by 

 explosions under water, when the conditions are such as to throw the water to a 

 considerable height. 



Lastly. The suddenness and energy of the operating force, as shown by the jets 

 being frequently projected considerably above the level of the upper water. 



The inquiry is one of some interest, and may serve to throw light upon those 

 anomalous effects which have been observed from time with regard to heavy seas 

 falling on a rocky shore, and the extreme height to which the water is occasionally 

 projected under those conditions. 



Two notable instances of this kind have been given by the engineers of the 

 English and Scotch Lighthouses. 



One at the Bishop Lighthouse, where a fog-bell weighing three hundredweight, 

 and fixed at a height of 100 feet above the sea, was displaced and thrown down to 

 the rocks below. 



