Methods of determining and calculating, fyc. 267 



Art. VIII. — On the methods of determining and calculating the 

 specific heats of certain solids, ivith some precautions to be ob- 

 served in the experiments; by Walter R. Johnson, Professor 

 of Mechanics and Natural Philosophy in the Franklin Institute 

 of the State of Pennsylvania. 



From the Journal of the Franklin Institute. 



The practice which formerly prevailed, of presenting to the pub- 

 lic, statements respecting the results of philosophical experiments 

 without a detail of the exact methods adopted for their attainment, 

 and the precautions employed to avoid error, has in many instances 

 involved the necessity of repetition — long and laborious, of what 

 ought, once for all, to have been definitively settled. The verif ca- 

 tion of a philosophical truth, by a method unhke any previously 

 employed, is a matter entirely different from the processes just re- 

 ferred to ; and however well we may be satisfied of a truth, estab- 

 lished in one manner, there will always be found both pleasure and 

 profit in attaining the same general conclusions, by methods and 

 considerations independent of each other. There is not perhaps 

 a better illustration of this remark than the variety of methods which 

 may be employed for determining the specific heat of solids. The 

 earliest was that of mixture, and consists in immersing the solid at a 

 known temperature, in water (or some other liquid,) at a tempera- 

 ture either above or below its own. The temperature lost by the 

 hotter body, and that gained by the cooler, will, with proper coitcc- 

 tions, give, when compared, the specific heat of the body under trial. 



The next method, that of Lavoisier, employs, instead of the rise 

 or fall of temperature in water, the latent heat of water passing 

 from a state of ice and the weight of this solid, which any other 

 given solid will melt while cooling from any known temperature 

 down to the melting point, is the measure of its specific heat, which, 

 being referred to the quantity of ice which a mass of water, equal 

 to that of the solid, would have melted in cooling the same number 

 of degrees, gives us the numerical expression of the specific heat of 

 the solid. 



The third method employs the cooling power of air, and the times 

 which will be required to depress the temperatures of the different 

 solids through a fixed range of the thermometer are taken as the 

 indices of the specific heat. This is the method employed by Pro- 



