200 Professor W. Tfiomson^ on the Origin [Feb. 29, 



All instrument was exhibited, by means of which the temperature 

 of a small quantity of water, contained in a shallow circular case 

 provided with vanes in its top and bottom, and violently agitated 

 by a circular disc provided with similar vanes, and made to turn 

 rapidly round, could easily be raised in temperature several degrees 

 in a few minutes by the power of a man, and by means of which 

 steam power applied to turn the disc had raised the temperature of 

 the water by 30° in half an hour. The bearings of the shaft, to the 

 end of which the disc was attached, were entirely external ; so 

 that there was no friction of solids under the water, and no way 

 of accounting for the heat developed except by the friction in the 

 fluid itself. 



It was pointed out that the heat thus obtained is not produced 

 from a source, but is generated; and that what is called into exist- 

 ence by the work of a man's arm cannot be matter. 



Davy's experiment, in which two pieces of ice were melted by 

 rubbing them together in an atmosphere below the freezing point, 

 was referred to as the first completed experimental demonstration 

 of the immateriality of heat, although not so simple a demonstration 

 as Joule's ; and although Davy himself gives only defective reasoning 

 to establish the true conclusion which he draws from it. Rumford's 

 inquiry concerning the " Source of the Heat which is excited by 

 Friction" was referred to as only wanting an easy additional ex- 

 periment — a comparison of the thermal effects of dissolving (in an 

 acid for instance), or of burning, the powder obtained by rubbing 

 together solids, with the thermal effects obtained by dissolving or 

 burning an equal weight of the same substance or substances in one 

 mass or in large fragments — to prove that the heat developed by 

 the friction is not produced from the solids, but is called into ex- 

 istence between them. An unfortunate use of the word " capacity 

 for heat," which has been the occasion of much confusion ever since 

 the discovery of latent heat, and has frequently obstructed the 

 natural course of reasoning on thermal and thermo-dynamic 

 phenomena, appears to have led both Rumford and Davy to give 

 reasoning which no one could for a moment feel to be conclusive, 

 and to have prevented each from giving a demonstration which 

 would have established once and for ever the immateriality of heat. 



Another case of apparent loss of work, well known to an 

 audience in the Royal Institution — that in which a mass of copper is 

 compelled to move in the neighbourhood of a magnet — was adduced ; 

 and an experiment was made to demonstrate that in it also heat 

 appears as an effect of the work which has been spent. A copper 

 ball, about an inch in diameter, was forced to rotate rapidly between 

 the poles of a powerful electro-magnet. After about a minute 

 it was found by a thermometer to have risen by 15° Fahr. After 

 the rotation was continued for a few minutes more, and again 

 stopped, the ball was found to be so hot that a piece of phosphorus 

 applied to any point of its surface immediately took fire. It is 



