Intelligence and Miscellaneous Articles. 407 



gations, performed partly in conjunction with M. J. T. Silbermann, 

 it has already been shown that such affinity may be expressed in 

 units of heat (calories) . 



The determination of the mechanical equivalent of heat was one 

 of the consequences flowing from an investigation of the kind just 

 described, inasmuch as I have succeeded in expressing in kilogram- 

 metres the work done (travail moteur) by molecular attraction (che- 

 mical affinity), in the same manner as the work done by universal 

 gravitation (weight) had already been exj^ressed. 



Thus, as announced in my last memoir, I have checked by inverse 

 experiments the results I had obtained, and on which I reposed con- 

 fidence. 



In fact, I raised 426 kilogrammes 1 metre by means of 1000 

 heat-units furnished by affinity and put into activity by the replace- 

 ment of hydrogen by zinc in hydrated sulphuric acid. I have now 

 shown how much heat is caused by the expenditure of work due to 

 the motive force of a previously raised weight, and I can substitute 

 the action of weight for that of chemical affinity. 



The experiments which I am about to describe present consider- 

 able analogy with those published by Mr. Joule, and which led him 

 to numerical results not very different from those since obtained 

 experimentally by other physicists. 



In my new researches, the work done by the fall of a weight is 

 expended upon a break, enclosed in a mercurial calorimeter (thermo- 

 metre a calories). In none of the experiments were less than 300 

 heat-units produced, this corresponds to a length of about 75 milli- 

 metres of the calorimetric tube. 



The arrangement of the apparatus is as follows : — 



The capacity of the calorimeter is about 5 litres. The break is 

 placed in a box 12 centimetres in length and breadth, and 18 centims. 

 deep. It is fastened by means of three milled-headed screws, by 

 which it may be raised or depressed at pleasure. This break, skil- 

 fully made by M. Santi of Marseilles, is 11 centims. wide and 16 

 centims. deep. It consists essentially of two vertical uprights, car- 

 rying in their sockets a steel axle. This axle carries a cylindrical 

 drum throughout its whole length, which is divided in the middle by 

 a disc, thus forming two reels, upon each of which a separate catgut 

 cord is wound. These cords are wrapped in opposite directions. 



A weight of 10-268 kilogrammes, hung at the extremity of one of 

 these cords, in addition to the permanent weight of 2 kilogrammes, 

 unwinds the cord to which it is applied, and at the same time winds 

 up the other cord, overcoming the tension in it, caused by another 

 permanent weight of 2 kilogrammes fastened to its extremity. This 

 tension is sufficient to ensure regularity in the unwinding. Thus, 

 when one cord is unwound, an equal length of the other is wound 

 up, and, by taking off the extra weight and hanging it at the end 

 of the cord which was before being wound up, the same effect is 

 produced, but in an o])posite direction. This motion of the two 

 weights in contrary directions is easily effected by means of two 

 pulleys, fastened independently of the break at a height of 3"5 metres, 

 each of whicli receives on its groove one of the cords as it leaves its 



