526 ^Mttiiij o/Bi:l>. 



jng tube. Tills fccoiid kind of augmentation was known to tlw ancients, though tliey pof- 

 fefled no good theory nor decifive experiments refpciling ir. The author endeavours to 

 eflabiifh a theory on the principle of virtual afcenfion combined with the prefTure of the at- 

 mofphcre. His <icduclions are confirmed by experiment, in which he has fucceeded fo 

 far as to feparate thd two cau-fes of augmentation, and afllgned to each their refpc>Slive de- 

 gree of influence. 



Citizen Vcnturi then proceeds to dilTcrent objects of enquiry, to which his principle 

 feemed applicable. He gives the theory of the water-blowing * machine, and he dcter- 

 niiues by calculation tlie quantity of air which one of thefe machines can afford in a given 

 time. He obfcrves, that the natural falls of water in the mountains always produce a local 

 wind ; and he even thinks, that the falling dreams in the internal parts of mountains arc 

 in fomc inftances the caufe of the winds which iflue from caves. He proves, by the facts, 

 that it is poffible in ccrtaiiij inftances to carry off, without any machinery, the waters from a 

 fpot of ground, though it may be fituated on a lower level than that of the channel which 

 is to receive the water. 



The whirlpools, or circular eddies of water fo frequent in rivers, are, according to the 

 theory of our author, the cH'ccl of motion communicated from the parts of the current which 

 are moft rapid, to thofe lateral parts which are lead fo. In the application of this principle, 

 he points out tlie circumftanccs adapted to produce fuch eddies at the furface or at the bot- 

 tom of rivers- Ue concludes, that every movement of this kind deftroys a part of the force 

 of the current, and that in a channel through which water conftantly flows, the height of 

 this fluid will be greater than it would have been if the dimenCons of the channel had beerj 

 uniformly reduced to the meafure of its fmalleft feiSlion. 



There is another kind of whirling motion fomewhat different In its nature from thefe 

 laft. It is produced in the water of a refervoir, wlien it is fuifered to flow through an hori- 

 zontal orifice. The author deduces the theory of thefe vortices from the doiflrine of cen- 

 tral forces. The form of the hollow funnel, which in this cafe opens through the fluid of 

 the refervcir, is a curve of the 64th fpecies of the lines of the third order, enumerated by 

 Newton. Theory and experiment both unite herein proving, that it is not only potlible, but 

 that there really exifts in nature a vortex, the concavity of which is convex towards the axis, 

 and of which the revolutions of its different parts follow the ratio of the fquare of the dif- 

 tance from the centre. Daniel Bernoulli was in the wrong, in his Hydrodynamics, to re- 

 proach Newton for having fuppofed a vortex to be moved according to this law. 



In the !afl place, the author confiders that lateral communication of motion which 

 takes pbce in the air as well as in the water. This is the caufe of fuch local and partial 



* Soufflet itrau. It is alfn called Iron^pf, bi;t we have no appropriate name for this engine in Erglifh. Tlie 

 reader may confult Lewis's PhilofopMcal Commerce of Ans, and Chapial's Elements of Clicniiftrv, for de- 

 icriptions. It confifls of an upright pipe, through which a ihowcrof water is made to fall. This (hower carriei 

 down a mafs of air with it, which is received beneath a kind of tub, and conducted to the furnace by meani 

 of a p'pe. The moft remarkable natural phenomenon of this kind is the fqual! at fea. When a cloud luddeniy 

 fulls m the form of rain, it drives down a portion of the atmofphcrc, which glides rapidly along the furface of 

 the fea, and is capable of fudJenly overfelting velfels, or carrying away their marts. It may calily be imagined, 

 that feamen are very attentive to look out for this phenomenon, and to gvard againft it in time by lowering theic 

 fails, &c. N. 



winds 



