ON THE FRICTION OF FLUIDS. 299 



charge nothing at all ; on the contrary, like the air in Hauksbee's experiment, 

 the water which it contains may be dragged after the stream in the larger 

 pipe. 



The bad effect of unnecessary dilatations, as well as contractions, in aque- 

 ducts and in pipes, may be understood from what has been already said of the 

 loss of force attendant on every change of velocity; a circumstance of a si- 

 milar nature sometimes happens in the animal economy. When an artery is 

 dilated so as to fsjrm an aneurism, it has been observed that the artery is 

 visually distended above the cavity; and this effect is easily understood from 

 the actual increase of resistance which the aneurism produces, united perhaps 

 with the previous debility of the artery... ,'U 



Mr. Gerstner, has found by some very accurate observations on the motion 

 of water in v6ry small pipes, that the resistance is considerably affected by 

 the temperature at which the experiment is performed; but in the cases of 

 rivers, and of such pipes as are commonly used in practice, no variations of 

 temperature, to which they can be liable, will produce any sensible effects. 

 His experiments indicate a resistance, where the tubes are very small, which 

 follows a law so different from that which is observed in more common cases, 

 that it appears to be owing to some other cause : this cause is perhaps the ca- 

 pillary attraction of the open end of the tube, and it is the more probable 

 that the resistance depends on some such circumstance, as there is reason to 

 think that the irregularity may be in great measure removed by placing the 

 tube wholly under water. 



