741 



WATERFALLS. 



WATERFALLS. 



742 



cloud. The same traveller relates that this " cloud formed from the 

 spray" of the Niagara falls was seen by him and his party on Lake 

 Ontario, at the distance of fifty-four miles, as " a small white cloud in 

 the horizon," which remained steadily fixed in the same spot, its 

 shape, as observed by a telescope, " varied every instant, owing to the 

 continued rising of the mist from the cataract beneath." But it is only 

 seen at such a distance, he adds, when the " air is very clear and there 

 is a fine blue sky." Weld also describes the now well-known appear- 

 ance of coloured bows in the spray, similar to rainbows, and for 

 which it will be convenient in this article to use that appellation. 



>" ^withstanding the production of these rainbows, proving the mist 

 to consist of separate drops of water, in the condition, in fact, of small 

 rain, it has frequently been described as vapour, and identified in nature 

 with fog and the clouds of the sky,* although rainbows do not occur 

 in them, and although we have no reason to believe that the conversion 

 of water into vapour can ever take place by mechanical action, however 

 viulent and continued. Were this possible, indeed, it could not but 

 take place at these falls, where the water is perpetually exposed to the 

 consequences of greater mechanical force than under any other circum- 

 stances whatever, either in nature or art ; where indeed all the circum- 

 stances are most favourable to such conversion, were it physically 

 possible. 



We have seen in the example of the Voring FOB, how enormous is 

 the force with which the spray into which the descending is divided by 

 the momentum with which it falls upon the still water, and partly, no 

 doubt by the resilient elasticity of the latter, is driven upwards. Such 

 spray, but greatly varying in magnitude, number, and approximation of 

 particles, and therefore in their aggregate effect and appearance, may 

 be produced under conditions in which water impinges with great 

 force upon water, or upon solid bodies, or solid bodies upon it ; also as 

 in storni-ppray, by the action of the wind on the surface of the sea, by 

 which, as by the perpetual action of waterfalls, persistent mist is fre- 

 quently occasioned. Further, it is produced to a sufficient extent for 

 the appearance of rainbows, when the waves of the sea, at their sum- 

 mits, curl and break into foam under the force of a breeze. But the 

 spray-mist of great waterfalls is in all probability occasioned, in 

 the greatest degree, and as consisting of the most minute particles, 

 by tlie violent bursting of the multitudinous air-bubbles already 

 described, forming the froth or foam of the falls, by which the films of 

 water inclosing the air are rent into minute dust, as it were, of water, 

 incalculable in the number of particles in a given space, and capable of 

 suspension in the air, like the globules of which the clouds of the sky 

 themselves consist. [CLOUDS.] 



These particles, however, diifer greatly from those of the clouds, and 

 the connection of their history with the subjects of the smallness of 

 the particles into which water is thus mechanically divisible, and the 

 true nature of the clouds, and of the globules or particles composing 

 them, is in several respect* instructive. The spray of waterfalls and 

 of the crests of waves consists of globules or particles of water, result- 

 ing, exclusively, from its mechanical division ; but the production of 

 perfect rainbows in it evinces that it is identical, within certain limits, 

 in respect of the magnitude of the particles, their distance from each 

 other, and their distribution in a given space, not with true cloud, but 

 with tha minute rain in which the rainbow of the sky occurs under 

 ordinary circumstancea. We have, therefore, in the production of that 

 meteor, a kind of measure of the magnitude, constitution, aud dis- 

 tribution of the particles, which, in all these cases, it is demonstrable 

 must be geometrically solid. 



We have, in several articles, already recorded our belief that the 

 globules constituting the clouds are not hollow, and our disbelief of 

 the existence of what has been termed ' vesicular vapour,' that is, of 

 vesicles of water (whether containing vapour or not), resulting from 

 the condensation of invisible vapour or water in its pure gaseous con- 

 dition. Sir J. F. W. Herschel (' Meteorology,' par. 92,) after describing 

 the production of mist or fog [Misi] by the precipitation of moisture 

 from the atmosphere, offers the following important observation on the 

 subject in question. 



" It is a favourite dogma with many meteorologists, that the particles 

 BO precipitated assume the form, not of drops, but of hollow spheres or 

 bubbles. De Saussure states that he has seen such floating before his 

 eyes in clouds and fogs on the Alps ; and the dusty appearance of the 

 vapour floating over a cup of coffee in the sunshine is adduced in 

 proof. The strongest argument in their favour, however (for there 

 is great room for optical illusion in such matters), is that adduced by 

 Kratzenstein, that the sun striking on a fog or cloud [t] produces no 

 rainbow, which it ought to do were the water collected in spherical 



Sir C. Lyell, for example, In his ' Travels in North America,' first identifies 

 the spray-cloud of Niagara falls with the clouds of the atmosphere, and then 

 with the undoubted steam-cloud rising from Etna (and other volcanoes), which 

 he also identifies with the clouds, regarding both phenomena as elucidating their 

 nature. But while the steam-clouds of volcanoes arc indubitably of the same 

 nature with the clouds of the atmosphere, the spray-cloud of Niagara, as shown 

 above, is different, notwithstanding iu appearance. 



[f The coloured bow similar to that produced by rain observed In misU lying 

 upon low ground*, a> mentioned in the article RAINBOW, is evidently caused by 

 the rlrops of wjtcr resulting from the aggregation of the aqueous p:uuclr 

 constituting the mitt, by the same process as the production of rain from 

 cloud*.] 



drops. This argument does not admit of a ready answer ; but the 

 difficulty, on the other hand, of conceiving any possible mode in which 

 such bubbles can be formed, disposes us to believe that the extreme 

 minuteness of the globules may perhaps be found to afford one, their 

 diameters being probably of an order comparable with the breadths of 

 the luminiferous undulations." * 



In the steam-cloud issuing from the boiler of a locomotive engine, 

 whether immediately above the funnel, when blowing off, or at a dis- 

 tance from it, or in the puffs of steam given off during the course of 

 the engine, no rainbow is ever visible, as the present writer can testify 

 from observation : they appear to be physically identical with the 

 clouds of the sky. With this agrees another point, the production in 

 all these cases of opalescent vapour [VAPOUR, OPALESCENT ; WEATHER], 

 which also is always caused in the clouds of nature ; intervening, as a 

 middle term, in the conversion of invisible vapour into cloud, and in 

 the resolution of cloud into invisible vapour. Its occurrence in both 

 processes may be observed in and about the clouds at almost all times 

 during the presence of the sun, or just before or after it; but less fre- 

 quently, and only under favourable circumstances, in moonlight. The 

 solar radiation, and the capacity of the air for more vapour on aud 

 above the upper surfaces of clouds, often render the intervention of 

 opalescent vapour invisible in that situation, but it may always be seen 

 in the reverse process, in the vapour-plane or vapour-zone [VAPOUR- 

 PLANE] at the base of masses of clouds, especially of cumuli. But the 

 production of opalescent vapour does not occur with the spray of water- 

 falls or waves. The reason seems obvious. The clouds of the atmo- 

 sphere and of the steam-engine consist of globules so minute that very 

 slight local changes of temperature will effect their resolution, and so 

 near to each other that the amount of opalescent vapour produced by 

 every one, individually, coalesces into an aggregate mass for all, so 

 that, though only momentary for each globule, it is persistent for the 

 mass, and therefore becomes visible. But the particles of the spray 

 are, comparatively, so large, that much greater differences of tempera- 

 ture are required for then- conversion into invisible vapour, and also so 

 distant, comparatively, from each other, that the local momentary 

 opalescence ceases, before, by the coalescence of that produced at many 

 points, it can become visible. 



We may safely conclude, therefore, it would appear, from all these 

 facts and arguments, and in corroboration of opinions generally but 

 not universally held, that the clouds are really composed of excessively 

 minute globules of liquid water, not hollow, and not consisting iu any 

 respect of vapour (though necessarily intermingled with it), which, 

 having resulted from the condensation of volumes of continuous vapour, 

 or of vapour no otherwise discontinuous than as occasioned by the 

 uniformly interspersed particles of the air, are formed at insensible 

 distances from each other ; and that these at length (under circum- 

 stances not altogether understood, and whether related primarily to 

 heat or to electricity is also uncertain) coalesce into much larger glo- 

 bules, or drops, exceeding in diameter the breadths of the luminiferous 

 undulations, and therefore capable, like the drops of waterfall- and 

 wave-spray, of exhibiting the rainbow. 



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 

 mingluig with them of pure transparent aqueous vapour, or air, or 

 both. 



The application to waterfalls of Professor Tyndall's observations on 

 the sound of agitated water, was founded merely upon his note iu 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 an u tln-omjli. 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-bladders 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 



* This is one of the very few cases in which it has been possible to consider tho 

 sensible magnitudes of the particles of ponderable matter as proportioned to the 

 measurable attributes of the ether, or to treat them as commensurate. Another 

 case has been pointed out by Dr. Faraday, who has shown that seven and a half 

 leaves of gold-leaf might be placed in the space occupied by a single undulation 

 of the red ray of light, and five in one of the violet ray ; so that a single leaf of 

 beaten gold occupies in average thickness no more than from one-eighth to 

 one-fifth part of a wave of light. (' I'roc. of Koy. Inst.,' vol. ii., p. 310 ; ' Phil 

 Traus.,' 1857, p. H7.) 



