12 Reynolds and Moorby, Equivalent of Heat. 



temperatures. He then yielded to the general wish in 

 the laboratory, and added such provision to the brake as 

 would admit of the measurement of the heat carried away 

 by the effluent water, but only for verifying the accuracy 

 of the balance of the brake as determined by mechanical 

 tests, which, owing to the friction of the shaft, was difficult 

 and only practicable to about one foot-pound. 



The supply of water to the brake came from the service 

 tank, loft. above the floor and 7ft. above the shaft ; the 

 tank being supplied through a ball-cock direct from the 

 town's main ; the pipe from the tank passing under the 

 floor to a point conveniently close to the brake, thence by 

 a branch rising vertically through the floor, in which there 

 is a hand-cock, and above this, at a height of 4ft. above 

 the floor, the automatic inlet valve. From this the pipe 

 turns horizontal until over the inlet into the brake, where 

 it ends in a mouthpiece facing the inlet, with which it is 

 connected by a flexible india-rubber pipe {Figs. I and 4). 

 The first provision made for measuring the temperature of 

 the entering water was an aperture in the bend over the inlet 

 valve with a vertical ^in. brass tube, soldered in, about 4in. 

 long ; this admitted an india-rubber cork, through the 

 centre of which a thermometer was passed down into the 

 pipe. This was subsequently replaced by a glass thermo- 

 meter chamber. 



To measure the temperature of the leaving water, it 

 was necessary, by means of a pipe fixed to the mouth of 

 the outlet valve, to lead the effluent stream above the 

 balancing lever of the brake and to one side of it. This pipe 

 was arranged so as to admit of the introduction of a ther- 

 mometer much in the same way as the other. In the first 

 instance, the extension-pipe and the thermometer were all 

 rigidly attached to the brake and moved with it, which 

 entailed a re-balance of the brake. Subsequently another 

 arrangement was made. The thermometers used in the 



