As a first step I placed the barometer at a distance of about 150 feet from the extreme western end of the Falls, on a flat rock as nearly as possible on a level with the top of the "talus" or bank of shingle lying at the base of the overhanging cliff, from which the cataract descends. This station was about 30 perpendicular feet above the pool basin into which the water falls. The mercury here stood at 29.68 inches. I then moved the instrument to another rock within 10 or 12 feet of the edge of the fall, where it was placed, by means of a levelling instrument, exactly at the same height as in the first instance. It still stood at 29.68 and the only difference I could observe was a slight continuous vibration of about two or three hundredths of an inch at intervals of a few seconds. So far, all was plain sailing; for, though I was soundly ducked by this time, there was no particular difficulty in making these observations. But within the sheet of water, there is a violent wind, caused by the air carried down by the falling water, and this makes the case very different. Every stream of falling water, as you know, produces more or less a blast of this nature; but I had no conception that so great an effect could have been produced by this cause. I am really at a loss how to measure it, but I have no hesitation in saying that it exceeds the most furious squall or gust of wind I have ever met with in any part of the world. The direction of the blast is generally slanting upwards, from the surface of the pool, and is chiefly directed against the face of the cliff, which being of a friable, shaly character, is gradually eaten away so that the top of the precipice now overhangs the base 35 or 40 feet and in a short time I should think the upper strata will prove too weak for the enormous load of water, which they bear, when the whole cliff will tumble down. These vehement blasts are accompanied by floods of water, much more compact than the heaviest thunder shower, and as the light is not very great the situation of the experimenter with a delicate barometer in his hand is one of some difficulty. By the assistance of the guide, however, who proved a steady and useful assistant, I managed to set the instrument up within a couple of feet of the "termination rock" as it is called, which is at the distance of 153 feet from the side of the waterfall measured horizontally along the top of the bank of shingle. This measurement, it is right to mention, was made a few days afterward by Mr. Edward Deas-Thompson of London, the guide, and myself with a graduated tape.