86 Relations between Chemical Change, [January, 



parts of a body. This disturbance or restoration of equi- 

 librium might be so contrived as to produce no outward effect 

 at all recognisable by our instruments. Take, for instance, a 

 cylinder, supported at the lower extremity, and pierced with 

 a number of vertical holes passing through it, through which 

 holes pass wires fastened to the upper surface of the 

 cylinder. Now a weight or weights hung to these wires 

 would cool the wires and heat the cylinder, and by increasing 

 indefinitely the number of wires and perforations of the 

 cylinder, the heat and cold produced would be so blended as 

 to be incapable of being detected. This is exactly the con- 

 dition in which water exists at its maximum point of density. 

 The heat and cold produced exactly balance each other. 

 Now let us take Joule's famous experiments, on which, one 

 may almost say, the doctrine of the mechanical equivalent 

 of heat is founded. He churned various liquids in a 

 calorimeter and measured the increase of temperature. But 

 in this kind of motion, as, perhaps-, in all cases of friction, 

 there is a pulling exertion of force, as well as one of pushing. 

 Behind the arms of the paddle-wheel in the churn the liquid 

 is pulled, and is pushed before them. Hence we might 

 expect cold to be produced as well as heat, but the thermo- 

 meter will only show the balance of heat over cold. From 

 these and such like experiments, therefore, we can draw no 

 trustworthy conclusion whatever as to the amount of dis- 

 turbance of equilibrium which has taken place. 



3. Now take again M. Favre's elaborate experiments 

 with a galvanic battery. He formed a galvanic circuit, in 

 which he placed an electro-dynamic engine. He placed the 

 battery in one calorimeter, and the engine in another. He 

 found that the battery working alone without the engine 

 produced 18,682 units of heat for every gramme of hydrogen 

 evolved. When the battery worked the engine, but without 

 raising any further weight, he found that the battery calori- 

 meter produced 13,888 units of heat, and the calorimeter in 

 which the engine was placed, 4679 units, making together 

 18,657 units ; whence he concluded that the other 25 units 

 were absorbed and disappeared in working the engine. He 

 next made the engine raise 131*24 kilos, a metre high, and 

 found then that the battery calorimeter showed 15,427 units 

 of heat, and the engine calorimeter, 2947, making together 

 18,374 units. Hence he concluded that the remaining3o8 units 

 were absorbed in the 131*24 kilogramme-metres of work. He 

 consequently deduced that the mechanical equivalent of heat 



was about -2 — -i_ or 426. Now let me give reasons for 

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