510
[Book V.
be supposed that a force so energetic—one that would rupture pipeswhicb convey water to our dwellings—wvould rend asunder most of thedelicate pores tbrough which it circulates ; and so it would were not tbeirdiameter so exceedingly small—-for the strength of tubes increases as theirbore is diminished.
The ascent of sap has been explained b y Endosmosis, or transit of bodiesthrough pores. See two interesting papers on this subject in the Journalof the Franklin Institute, vols. xvii and xviii, by J. W. Draper, now Prof,of Chemistry in the New-York University.
Water Spouts constitute a peculiar dass of nature’s contrivances forraising water. Electricity is supposed to have a Controlling influence intheir formation ; but the mode by which it acts is not clearly understood.More water is draum up by them within the same space of time than byany other natural device. The liquid appears to be borne up the vortexmechanically as solid substances are raised by whirlwinds, except thatit is broken by masses of air rushing into and mixing with it. Afterarriving at the top of the spout, it is dispersed by lateral currents of wind.A drop of water suspended from the conductor of an electrifying machineis supposed to exhibit a miniature water spout. When a vessel of wateris placed under it, and the machine put in Operation, the drop assumesthe various appearances of a spout in its rise, form, and mode of disap-pearance. Clouds act as cisterns in holding water raised by evaporation;but in water spouts they perform a more singulär part, since they aremoulded into visible pipes, through which volumes of liquid are conveyedas securely as through those made of solid materials.
Although the rise of sap in trees is attributed to endosmosis, there isreason to believe that capillary attraction takes part in the process, aswell as in a thousand other operations of nature. When one end of asmall glass tube is placed in water, the liquid rises within it; and theheight to which it ascends in different tubes, is inversely as their diame-ters. The phenomenon is more or less common to all liquids when thetubes dipped in them are made of such materials as they readily unitewith. This condition is necessary, otherwise the liquid would be de-pressed. Water rises higher than other liquids in glass tubes ; and asthese Instruments are transparent, they are always adopted in experimentson this subject.
The phenomenon of capillarity has exercised the ingenuity and learn-ing of the most eminent philosophers, and various are the causes to whichthey have attributed it. Some supposed the atmospheric pressure lesswithin the tubes than without. Others imagined an unknown fluid cir-culating through them that bore the liquid up; and some ascribed it tomoisture on the inside of the tubes. An attractive force existing betweenthe glass and the water is now more generally admitted ; and hence intubes of very small bore, it is said, the glass being nearer the water, at-tracts it more powerfully, i. e. raises it higher—-other writers think theeffect is due to electricity. The subject is admitted to be an intricate one,and the manner in which it has been handled by scientific men, has notrendered it very accessible to ordinary readers. Without looking forultimate causes, the phenomenon, like that of an increased discharge,through diverging ajutages, may be traced to the relative properties ofthe liquid and the material of the tube, and to the force with whichparticles of liquids cohere among themselves.
Capillary attraction is exhibited in a great variety of forms. Particlesof water, like those of all other liquids, require some 1 force to separatethem. A needle or film of lead while dry, will float; and myriads of