488 Great RelardatioH of Fluids through irregular Pipes, 



Experiment XXIV. The circular orHlce A, fig. 1 2. has the form of the contradllon of 

 the vein, and the remaining part of the tube is interrupted by various enlargements of its 

 diameter. This tube is applied to the aperture P, fig. i . The dimenfions of its parts 

 meafured in Hnes are as follows. Diameter at A = 1 1,2. Diameter at B, C, F, G, &c. =r 9. 

 Length of B C = F G, &c. = 20. Lengtli of C D = E F = G H, &c. = 13. Diameter 

 of the enlarged parts = 24. The length of each of the enlarged parts was variable. The 

 firft time of trial it was 38 lines, the fecond 76, and therefult of the experiment was the 

 fame in both cafes. ' 



Number of enlarged parts. Time during which four cubical feet Iflued out, 



o 109" 



I • 147" 



3 ^92" 



5 240" 



I afterwards applied to the fame orifice a tube, having the fame form, and the fame diameter, 

 as ABC, but cylindrical throughout, without any enlargements, and its length was 36 inches, 

 the fame as that of the tube with five enlarged parts ; in this cafe the expenditure of four 

 cubical feet was made in 148". 



When the fluid pafles from C to the middle of the enlarged part D E, part of the motion 

 is diverted from the direftion C F towards the lateral parts of the enlargement. This part 

 of the motion is confumed in eddies, or againft the fides. Confequently there remains fo 

 much the lefs motion in the following branch F G. This is alfo the caufe which deftroys, 

 or weakens, the pulfe in the arteries beyond an aneurifm. 



From this confideration we are juftified in concluding, that if the internal roughnefs of 

 a pipe diminifhes the expenditure, the fridlion of the water againft thefc afperities does not 

 form any confiderable part of the caufe. A right-lined tube may have its internal furface 

 highly poliihed. Throughout its whole length, it may every where poflefs a diameter greater 

 than the orifice to which it is applied ; but, neverthclefs, the expenditure will be greatly re- 

 tarded if the pipe fhould have enlarged parts, or fwellings. This is a very interefting cir- 

 cumftance, to which, perhaps, fufficient attention has not been paid in the conftruftion of 

 hydraulic machines. It is not enough that elbows and contractions are avoided ; for it may 

 happen, by an intermediate enlargement, that the whole advantage may be loft, which may 

 have been procured by the ingenious difpofitions of the other parts of the machine. 



PROPOSITION VIII. 



In the machine for blowing by means of a fall of water , the air is afforded to the furnace by thr 

 accelerating force of gravity and the lateral communication of motion, combined together. 



The Academy of Touloufe, in the year 1791, invited philofophers to determine the caufe 

 and the nature of the ftream of air which is produced by the fall of water in certain forges. 

 I propofe, in this place, to develope the complete aftion of this kind of blowing apparatus, 

 and to afccrtain the beft form of conftruiStion. Kircher is the firft I know of who has ex- 



plamed 



