ON THE REGULATION OF HlTDRAULIC Ft>IlC"E!S. 31/ 



it would be necessary to bend it upwards at the extremities, in order to kee{» 

 it always full : but in this case the accumulation of the air would be extremely 

 inconvenient, since it would collect so much the more copiously, as the water 

 in the upper part of the pipe would be more free from pressure, and neither of 

 the methods which have been mentioned would be of any use in extricatin(» 

 it. It has been usual in such cases to force a quantity of water vioientlv 

 through the pipe, in order to carry the air with it; but perhaps the same effect 

 might be produced much more easily, by making a small airtight valve -in the 

 upper part of the pipe, opening outwards, and a stopcock immediately before 

 it: the stopcock being suddenly turned as often as might Ire necessary, the 

 momentum of the water in the pipe would ptobably carry it forwards with 

 sufficient force to throw out the air ; or, if it were necessary external pressure 

 might be added, and the air might even in this manner be discharged by the 

 valve much more readily than without it. But it might be still simpler to 

 have a pretty large vessel of water screwed on to the pipe, which would not 

 be filled with air for a considerable time ; and which, when full, might be taken 

 off and replenished with water. (Plate XXI. Fig. 285.) 



The diameter of a pipe, required for conveying a given quantity of water to 

 a given distance, may be calculated from the experiments of Mr. Buat, which 

 have been already mentioned. Pipes are usually made of wood, of lead, or of 

 cast iron ; but most commonly of lead; and of late tinned copper has beea, 

 employed with considerable advantage. A pipe of lead will bear the pressure 

 of a column of water 100 feet high, if its thickness be one hundredth of its 

 diameter, or even less than this; but when any alternation of motion is pro- 

 duced, a much stronger pipe is required, and it is usual to make leaden pipes" 

 of all kinds far thicker than in this proportion. 



The form and construction of stopcocks and valves are very various, ac- 

 cording to their various situations and uses. Stopcocks usually consist of a 

 cylindrical or conical part, perforated in a particular direction, and capable of 

 being turned in a socket formed in the pipe, so as to open or shut the passage 

 ©f the fluid, and sometimes to form a communication with either of two or 

 more vessels at pleasure. A valve is employed where the fluid is to be allowed 

 to pass in one direction only, and not to return. For Avatcr, those valves 

 arc the best which interrupt the passage least; and none appears to fulfil 



