Minute globules or particles of water, it is now evident, exist of several orders of magnitude, each order having characteristic proper ties, whether of its own, or arising from the mutual distance of the particles and their consequent number in a given space, or from the both..
glipg with them of pure transparent aqueous vapour, or air, or The application to waterfalls of Professor Tyndall's observations on the sound of agitated water, was founded merely upon his note in the ' Vacation Tourists,' cited above, the writer of the above remarks on the physics of the subject not having seen the paper in the Philo sophical Magazine' referred to in that note, until after they were in type. Professor Tyndall, after alluding in that paper (' Phenomena of a Water-Jet') to the roar of the ocean as being caused by the bursting of bubbles, himself applies his inferences to waterfalls in the following manner :—" It is the same as regards waterfalls. Were Niagara con tinuous and without lateral vibration, it would be as silent as a cataract of ice. It is possible, I believe, to get behind the descending water at one place [this is readily practicable, and frequently done]; and if the attention of travellers were directed to the subject, the mass might perhaps be seen through. For in all probability it also has its con tracted sections,' after passing which it is broken into detached masses, which, plunging successively upon the air-bladdera formed by their precursors, suddenly liberate their contents and thus create the thunder of the waterfall." Professor Magnus, of Berlin, it appears, was the first to account for the production of bubbles when water is poured into a glass,—the same physical phenomenon as their production by waterfalls. It is
briefly thus, as he proved by experiment : a concavity is farmed by the falling water at the point where It strikes the water below ; this closes In as soon as the least motion has been imparted to the surface, and the air within it is carried downwards. It will readily be seen how illustrative this explanation is of a part of Capt. B. Hall's account of the air-bubbles at the Niagara falls, and of the applications of it above ; but no part of the air, it must be inferred from the experi ments of Professors Magnus and Tyndall, is carried down by adhesion to the water.
In another part of his paper, Professor Tyndall, illustrating experi mentally the subject of the contracted vein [Ilvneonesealics, col. 774], describes the resolution of the vein or stream of water, after passing the contracted section, into detached masses; and observes, "Follow ing the jet downwards, we find that these masses become more and more attenuated ; and were the height sufficient, they would finally appear as a kind of waterdust, an example of which on a large scale is furnished by the Staub-barh , near Lauterbrunnen, in Switzerland. Traveller" usually attribute the breaking up of the Staub-bach to atmospheric resistance, but the latter has comparatively little to do in the matter ; were the surrounding space a vacuum, the same would be exhibited." This indicates an additional and very effective cause of the production of waterfall 'spray, and is probably applicable to the phenomena of the Poring Fos, noticed above, which appear not to be accurately understood. (See ' PhiL Mag.' Series 4, vol i. p. 1, and p. 105.)