102 TRANSMISSION OF PRESSURE. HYDRAULIC PR] 



face of the bottle which has the same dimensions as 

 cork, has to bear the same pressure as that which is appl 

 to the cork. In a common wine-bottle the area of a sec 

 tion of the neck, and hence of the cork,- is about 3 squar 

 centimetres, and the internal surface of the bottle abon 

 450 square centimetres. This surface contains therefor 



' = 150 surfaces, each equal to that of the cork, an 

 o 



has to bear a pressure 150 times as great. This fact ma 

 also be expressed thus : 



Pressure is transmitted in a liquid in such a manm 

 .that the pressures exerted upon different surfaces are pn 

 portional to the areas of the surfaces. 



The hydraulic press is an application of the law < 

 the transmission of pressure in liquids. Two hollo 

 cylinders of different diameters, c and (7, fig. 113, ai 

 connected by a tube r ; in each cylinder a solid piste 

 moves water-tight. The smaller piston, or plunger, 

 may be pressed down with the hand or by means of 

 special lever; the larger piston, or ram, S, carries a cas 

 iron plate, P 1 ; any body placed on this can be press* 

 against a second plate, P 2 > supported by strong colurar 

 The portion of both cylinders below the pistons beii 

 filled with water, the pressure applied in a downwa 

 direction to the plunger is transmitted to the ram, ai 

 forces it upwards. If the diameters of the pistons be 2 

 and 20 cm , their sections are 1 x 1 x 3'14 = 3 cm> 14, ail 

 10 x 10 x 3-14 = 314 cm respectively, and the pressu 



314 

 upon the ram is ^ -- = 100 times as great as tlr 



upon the plunger. Thus a pressure of 50 kgr upon t 

 plunger produces a Pressure of 5,000 kgr upon the raj 



