174 Exj'eii'iuHtj on the laleral Cotninunicathn of Alotlcn In Fluids. 



EKpetimeiit 2. Bring fome very light or moveable bodies near the jet of w^ter P Y, fig. T, 

 which ifTuts from the aperture P, and falls from a certain height E into the inferior vefl'el 

 RT. It is feen that thcfs bodies are carried, along by the air which defcends with the jet 

 P Y. Purt of this air is carried along and plunged into the water of the inferior veffel. 



Thefe experiments clearly prove, that the fluid which ifi'ues by B C, fig. 2, imprelTes its 

 motion on the lateral parts N K ; net by impelling them towards P Q^, but by carrying them 

 along with itfelf towards S. 1 call this the lateral communication of motion in fluids. 

 Newton was acquainted with this communication, and has deduced from it the propagation 

 of rotatory motion from the interior to (he exterior ftrata of a whirlpool. Is this lateral 

 communication of motion occafioned by the vifcidity or mutual adhefion of the parts of the 

 fluid, or their mutual engagement or intermixture, or the divergency of thofe parts which are 

 in motion ? We may perhaps be able to give fome account of this v/hen we (hall have ken 

 the cffl6ls; but in the mean time, whatever may be the caufe, let us take the eS^Q. as ex- 

 perience points it out; let us confider it as a principle, and endeavour to apply it to fome 

 particular cafes in order to afcertain the refult. 



The firft circumftance to which I propofe to apply this principle is the increafe of expen- 

 diture of fluid iffuing out of an orifice fitted with additional tubes. 



Propofiticn 2. If that part of an additional cylindric tube which is nearefl: the fide of the 

 refervoir be contracted according to the form of the contradted vein of fluid which ifTues 

 through a hole of the fame diameter in a thin plate. The expenditure will be the fame as if the 

 tube were not contrafted at all. It is well known, that when the water of a refervoir is 

 AifFered to flow through a circular orifice in a thin plate, the fluid vein which forms the jet 

 becomes contraded at a fhort diftance from the orifice ; and the diameter of the contrafted 

 vein is nearly 0,8 of the diameter of the orifice. Poleni firft obferved, that by applying an 

 additional cylindric pipe to the orifice, of the fame diameter as the orifice itfelf, and from 

 two to four times that length, the expenditure is increafed from lOO to 133. To account for 

 this augmentation, he fuppofes that the fluid vein is lefs contra6ted in pipes than after pafling 

 through the thin plate. The fuppofition was not unreafonable ; but it could not apply to the 

 cafe announced in this propofition. I fliall proceed to give the particulars in the following 

 experiment. 



Experiment 3. To the aperture P, of fig. i, I applied a circular orifice 1 8 lines in diameter, 

 pierced through a thin plate. Four cubical feet of water flowed into the veflel Y in 41 

 feconds. 



I then applied to the orifice a cylindric tube of the fame diameter, and fifty-four lines 

 long. The four cubic feet flowed out in 31 feconds. 



Inftead of this fimple cylindric tube, I applied the compound tube of fig. 5 ; the parts 

 of which have the following dimenfions in lines : AC=GI = MN = i8; DF = 14,5; 

 AB=ii;BG=io; GM=37; AM =58. With this compound tube the expendi- 

 ture of four cubic feet of water was made in 31 feconds, as with the fimple cylindric tube. 



The form of the conical portion A C D F was nearly the fame as that of the contradion 

 of the vein which ifllies through a thin plate. The vein muft therefore have pafiTed through a 

 contradlion nearly equal to that of the contracted vein from a thin plate j the expenditure 



' never- 



