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XLIV. An Improved Design for the Friction Cones of Searle's 

 Apparatus for the Mechanical Equivalent of Heat. By 

 H. P. Waran, M.A., Government Scholar of the Uni- 

 versity of Madras *. 



IN Dr. Searle's well-known apparatus we have two cones 

 of gun-metal, one inside the other, ground to a good fit 

 so that by rotating the outer cone about the inner the fric- 

 tion between them converts the work done into heat, and it 

 is estimated by noting the temperature rise of water con- 

 tained in the inner cone. Though the apparatus is extra- 

 ordinarily efficient for its size and simplicity, yet it is not 

 without a few drawbacks. The present modification is an 

 attempt to get over them. 



The thickness of the walls of each of the metal cones is 

 about 3 mm., and the heat generated by friction at the 

 surface of contact has to be conducted through this thickness 

 of metal before it can raise the temperature of the water. 

 And in an ordinary laboratory experiment to minimise the 

 effects of heat loss due to radiation the temperature rise is 

 kept very low, and consequently the temperature gradient 

 in the metal is small and the rate of conduction of heat to 

 the water is slow. Further, the employment of water with 

 its low conductivity of heat as the liquid to absorb the heat, 

 makes the situation only worse. In the presence of these 

 drawbacks very vigorous stirring of the water in the inner 

 cone is essential to ensure a rapid equalization of temperature 

 throughout the system, and in that stirring probably we are 

 adding an amount of unmeasurable work and consequently 

 heat to the system, which is probably very small. Further, 

 this is an extra operation the experimenter has to do very 

 efficiently, in addition to his duties of turning the wheel at 

 a steady rate with one hand and noting down the thermo- 

 meter reading with the other. 



The following is ah improved design for the cones calcu- 

 lated to overcome the above disadvantages. 



As will be evident from the diagram, the inner cone I is 

 made open at the bottom, and has, in addition, a few helical 

 grooves G cut on the contact surface of the inner cone, 

 these grooves terminating in a ring-channel S cut near 

 the top of the cone. From this channel a few holes are 

 drilled sloping inwards into the cone. The grooves Gr are 

 cut sloping upwards in the direction of rotation of the outer 

 cone. Further, for the liquid in the cones any essential oil 

 of known specific heat and large conductivity for heat is- 

 * Communicated by the Author. 



