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ON A LECTURE-ROOM APPARATUS FOR THE DETERMINATION OF
THE MECHANICAL EQUIVALENT OF HEAT. BY H. J. PULUJ, ASSISTANT IN THE IMPERIAL MARINE ACADEMY, FIUME.
The apparatus is of very simple construction, consisting essentially of a calorimetric and a dynamometric portion, suitably connected with an oscillation-machine such as is found in every physical 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 machine 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 pulley on a level with it, over which a thread, to which a scale is suspended, 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 surface 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 include 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 calorimeter, 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 experiment proper lasting but 30–60 seconds, on which account the apparatus may be recommended for lecture-experiments.--Kaiserl. Akad. der Wissenschaften in Wien, math.-naturw, Classe, April 15, 1875.