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experiments that heat has a definite equivalent of mechanical power, 

 and also of electrical current ; and the other, applying to these facts 

 the resources of theory, has extended this principle to chemical forces 

 with fair promise of success. The experimental verification of his 

 reasoning, and the collection of numerical data, promising as they 

 seem to do, no less than the power of including the whole doctrine 

 of affinity within the range of calculation, appear of such importance, 

 that the Committee have considered the subject worthy of a grant, 

 and have devoted to it a sum of fifty pounds, the amount required. 



They have also placed thirty pounds at the disposal of Mr. Joule 

 for an analogous purpose, the investigation of the change of volume 

 which takes place in iron on which magnetism is induced, indicating, 

 as it seems to do, a close connection between that energy, and the 

 tensile and compressive forces of the metal. 



A grant of fifty pounds has also been made to Dr. Tyndall, to 

 examine the conducting power of crystals for heat, as compared with 

 their transmission of it. In this last respect, as was long since shown 

 by Melloni, they differ widely ; thus rock salt is almost perfectly 

 diathermic or transparent for heat ; alum as decidedly the reverse ; 

 but the propagation of heat by radiation diflfers so widely from that 

 by conduction, that it is important to inquire, what differences exist 

 as to the latter ; and the more so, because it has been shown by 

 de Senarmont, that in most crystals the conducting power varies in 

 different directions. 



An equal sum has been granted to Mr. Dale for researches in the 

 same direction as those of Dr. Kohlrausch (lately made known to 

 the English reader by Dr. Tyndall's translation), respecting the 

 electric tension of the various parts of the voltaic circuit. They 

 belong to the most refined and delicate class of observations, and 

 are peculiarly open to various causes of deception ; while the in- 

 formation to be derived from them is of an order, whose value is 

 only now beginning to be fully appreciated. It is a very narrow 

 view of their value to regard them merely as criteria between the 

 contact or chemical theory of the voltaic battery ; that question will 

 apparently be soon forgotten in the wider system, to which I have 

 already alluded as indicating the correlation of all these corpuscular 

 forces. Every new fact, every wider glance which we obtain over 

 the world of physics, shows that man can only transform, or modify 

 force, but not create it : even when his own will generates motion 

 in his own body, it does so only by the subversion of chemical 

 affmity, in the components of that body, and so in every other 

 instance. The voltaic current, whatever it may be, can do a continu- 

 ous and definite amount of chemical or calorific work ; its power 

 therefore must be derived from an equivalent and continuous expen- 

 diture of some other force. Such an expenditure, as Faraday has 

 well remarked, cannot be afforded by mere contact, but is unequi- 

 vocally presented by the chemical action of the battery. In the 

 common electrical machine the friction seems to act in producing a 

 succession of changes in the elastic forces of the rubbing surfaces, 

 and the intense electricity thus evolved, shows by its difference of 



