Manchester Memoirs, Vol. xlviii. {igo^), No. 7. 19 



steam on admission to the steam chest and at exit from 

 the exhaust spaces, and to keep these pressures constant 

 the receivers should be large. 



The machine could be made double-acting by 

 providing it with two valves one on either side of the 

 piston and thus alternating loads could be applied. A 

 much simpler method would be to put a cylinder cover 

 above the piston and keep the space between it and the 

 piston at any constant desired pressure. In this way any 

 limits of either tension or compression can be obtained. 



The principal advantages of this machine are : 



(i) There are no reciprocating parts, and hence no 

 lubrication or inertia disturbances (in order to 

 make sure that there are no appreciable inertia 

 forces all the parts connected to the specimen 

 should be made as light as possible consistent 

 with ample strength). 



(2) The highest frequencies of loading can be easily 



obtained. 



(3) The lubrication is very simple. 



(4) The frequency and loading can be varied inde- 



pendently of each other. 



(5) Simple compression or simple tension between 



any limits can be obtained. 



(6) Any limits of alternate tension and compression 



can be obtained by a slight modification of the 

 machine. 



(7) The specimen does not move and can therefore 



be kept under observation, microscopic or other- 

 wise. 



(8) The specimen can be made to carry an electric 



current or be placed in a magnetic field. 



