CHAPTEE I.
Subjects treated in the fiftfr book—Lateral communication of raotion—This observed by the ancients_
Wind at the Falls of Niagara—The trombe described—Natural trombes—Tasting hot liquids—Water-gpouts—Various operations of the human mouth—Currents of water—Gulf stream —Large rivers—Ad-ventures of a bottle—Experiments of VentHri—Expenditure of water from various formed ajutages—Contracted vein—Cause of increased discharge from conical tubes—Sale of a water power—Regulationof the ancient Romans to prevent an excess of water from being drawn by pipes from the aqueducts.
In this book we propose to notice some devices for raising water thatare either practically useful, or interesting from their novelty or the prin-ciples upon which they act. An account of siphons is added, and alsoremarks on cocks, pipes, valves, and other devices connected with practicalhydraulics.
A fluid moving in contact with another that is comparatively at rest,drags along those particles which it touches, and these by their mutualadhesion carry their neighbors with them; the latter also communicatethe impulse to others, and these to more aistant ones, until a large massof the fluid on both sides of the motive current is put in motion. Whatevermay be the process by which this is effected, or by whatever name theprinciple involved may be called, (lateral communication of motion or anyother) there is no question of the fact. The Operation moreover is notconfined to any particular fluid, nor is it necessary that the one movedshould be of the same nature as the mover: thus air in motion moveswater and other liquids as well as air, and aqueous currents impart motionto aeriform fluids as well as to Standing waters. A stream of wind froma bellows bears with it the atmospheric particles which it touches in itspassage to the fire—i. e. it sweeps along with it the lining of the aerialtube through which it is urged. Blowing on a letter sheet to dry the ink,or on sealding food to cool it, brings in contact with these substancesstreams of other air than what issues from the thorax.® The operationsby which the man in the fable blew hot and cold “ out of the same mouth ”
a Does not the same principle perform an important part in respiration ?—the lungsnot being wholly inflated by air directly in front of the iips, where partieles of thatpreviously exhaled might still linger, but also by currents flowing in from all sides ofthe mouth or nostrils.