416 Intelligence and Miscellaneous Articles, 



N A LECTURE-ROOM APPARATUS FOR THE DETERMINATION OP 

 THE MECHANICAL EQUIVALENT OF HEAT. BY H. J. PULUJ, 

 ASSISTANT IN THE IMPERIAL MARINE ACADEMY, PIUME. 



The apparatus is of very simple construction, consisting essen- 

 tially of a calorimetric and a dynamometric portion, suitably con- 

 nected with an oscillation-machine such as is found in every physi- 

 cal cabinet. 



The calorimetric part is formed by two hollow truncated cones 

 of cast iron, one fitting into the other, the inner not quite reaching 

 to the bottom of the outer, and appearing a little outside of it. 

 The outer cone can be fixed coaxially in the vertical bobbin of the 

 machine. The inner cone contains mercury. If the machir e is put 

 in motion and the inner cone fixed, heat is generated by the friction 

 of the surfaces. 



An arrangement which is an inversion of Prony's check serves 

 for the measurement of the work which is converted into heat. On 

 the wooden lid of the inner cone a light wooden beam is screwed 

 horizontal. A perforation passing through the beam and lid receives 

 the thermometer. At some distance from the beam is a fixed pul- 

 ley on a level with it, over which a thread, to which a scale is sus- 

 pended, is slung and is fastened to the end of one arm of the beam ; 

 the other arm serves as a counterpoise. "When the machine is set 

 in motion, the interior face of the outer cone rubs against the sur- 

 face of the inner one, and tends to turn the beam which is fastened 

 to the latter in the direction of the motion. "With a certain load 

 the horizontal part of the thread and the axis of the beam will in- 

 clude a right angle. From the length of the beam-arm, amount of 

 the load, and number of rotations the work converted into heat, and 

 from the water-value of the calorimeter and the rise of temperature 

 the quantity of heat generated, can be calculated. 



The memoir contains also the development of the theory of the 

 apparatus, taking into consideration the heat radiated from the ca- 

 lorimeter, and, finally the numerical calculation of the values of the 

 mechanical equivalent of heat from 28 experiments. The mean of 

 those numbers, 425*2, with the mean error + 5*4, is in excellent 

 accordance with Joule's result, 424*9, and may be regarded not only 

 as a fresh corroboration of it, but also as a measure of the accuracy 

 with which the experiments can be conducted by means of this 

 simple apparatus ; and these occupy but very little time, an expe- 

 riment proper lasting but 30-60 seconds, on which account the ap- 

 paratus may be recommended for lecture-experiments. — Kaiserl. 

 AJcad, der Wissenschaften in Wien, math.-naturw. Classe, April 15, 

 1875. 



