ON TQE HEAT DEVELOPED IN COMBUSTION. l\\ 



surrounding air; while on the contrary it is heated by these 

 elastic fluids, whenever it is at a lower temperaturethan they 

 are: by arranging matters so, that the temperature of the 

 water in the receiver shall be a certain number of degrees, 

 5° for instance, below the temperature of the air at the be- 

 ginning of the experiment; and putting an end to the 

 experiment, as soon as the water in the receiver has ac- 

 quired a temperature precisely the same number of degrees 

 higher than the air; the receiver will be heated by the 

 air during half the time of continuance of the experiment, 

 and cooled by it during the other half: so that the calorific 

 and frigorific effects of the air on the apparatus will coun- 

 terbalance each other, and produce no perceptible effect on 

 the results of the experiments; consequently they will 

 require no correction. 



When we are making experiments to elucidate natural Better to avoid 



phenomena, it is always more satisfactory to avoid errours, or compensate 



. errour, than, 



or to compensate them, than to trust to calculation tor corr ect it by 

 appreciating their effects. calculation. 



As the law of the variation of the specific heat of water a sma n range 

 at different temperatures is not known, and as we have of the therm °- 

 but an imperfect knowledge of the true measure of the 

 intervals of temperature marked by the divisions of our 

 thermometers, to prevent the effects, that our uncertainty 

 on these points would have on the subject of inquiry, I 

 took care to make my experiments in a room, where the 

 temperature varied very little, and to confine them to a few 

 degrees of elevation of the temperature of the water in the 

 receiver. 



It is true, I made some experiments in a room where Other exper:- 

 the air was much colder, and in which I employed ice men ' s » 

 instead of water to fill the receiver; but these experiments 

 were for a particular purpose, and are not classed with the 

 others. Besides, they iifver afforded such uniform and sa- 

 tisfactory results, as those made under other circumstances. 



It has been fully proved, not only by the results of my Freezing of a- 

 experiments, but by the experiments of others also, that qucous vapour 

 the vapour of water in contact with ice frequently freezes, 

 while this same ice is melting, by the heat, or that its thaw 

 appears fully established. 



