TO PHYSIOLOGY AND PATHOLOGY. 43 



their equivalent weights. It is a well known fact, that different bodies receive a 

 different amount of heat at the same temperature. Equal weights of sulphur, iron, 

 and lead, heated to the boiling point of water, when brought in contact with ice, 

 melt a certain quantity of it, but the amount of water produced under these 

 circumstances is very different. 



If the quantity of heat were equal in the three bodies, the weight of melted ice 

 must amount Wthe same in all, but the unequal effect which is here observed 

 proves the want of uniformity in the active cause. Sulphur melts six and a half 

 times as much ice as lead, while iron melts four times as much. It is perfectly 

 clear, that when we heat sulphur, iron, and lead at the same difference of tempe- 

 rature, say for example, from (60 to 400) with the same spirit lamp, we should 

 have to consume half an ounce of spirit to heat lead, three ounces and a quarter 

 of an ounce for the same quantity of surphur, and nearly two ounces for an equal 

 weight of iron. 



These differences in the amount of heat required to raise equal weights of 

 different bodies to the same degree of temperature, and which are peculiar to each, 

 are termed their specific heats. From the knowledge of the unequal amount of 

 heat, which bodies of equal weights contain, at a similar degree of temperature, 

 we obtain an invaluable rule of proportion, by which we are able to reckon the 

 weights of sulphur, lead, and iron, which contain a like quantity of heat ; thus, for 

 instance, 16 parts of sulphur will melt as much ice as 28 parts of iron, and 104 

 of lead, at equal temperatures. These numbers are the same as the combining 

 weights or the equivalent numbers. Like equivalents of these and many other 

 bodies take up a similar amount of heat in order to raise themselves to an equal 

 temperature, and if we consider the equivalents as the relative weights of atoms, 

 it is clear that the amount of heat, which each atom takes up, or gives off under 

 similar conditions, is the same for every atom, and when expressed in numbers, 

 is inversely proportionate to the weights of the atoms. 



It certainly is a singular result that the amount of ice which a body melts, 

 should have served in many cases to define and establish the relations of weight, 

 in which this body combines with others. 



SPECIFIC HEAT AND TONE OF GASES. 



It may appear still more singular to many that this property, in aeriform bodies, 

 of taking up and giving off heat, stands in a definite relation to the tone produced 

 by blowing gas through a pipe or flute. This is so truly the case, that a celebrated 

 naturalist, Dulong, was able to compute by the irregularity of tone, the amount of 

 heat which in a constant volume the gases give out on pressure, and take up on ex- 

 pansion. In order to obtain a clear insight into this remarkable connection, we 

 must recall to mind, the beautiful idea of La Place, concerning the connection of 

 the specific heat of a gas, with its power of propagating sound. It is known that 

 Newton, and many mathematicians since his time, have in vain sought to, establish 

 a formula to guide us in the observation of the velocity of sound. The formula 

 that was calculated, closely approximated to the result of observation, but there 

 was always an inexplicable difference. As now propagation of sound takes place 

 by means of the vibrations of the elastic molecules of the atmosphere, in conse- 

 quence of pressure, and subsequent expansion, and as, on pressing together the 

 air, heat is liberated, while, on the expansion of the atmosphere, heat is absorbed, 

 La Place conjectured that this phenomenon must have an influence upon conduct- 

 ing the sound ; and it was proved, that by making a correction for the specific heat 

 of the air, the formula of the mathematician was free from all errors, and was an 

 accurate expression of the velocity observed. 



If now we compute the velocity of sound according to the Newtonian formula 

 (that is, without reference to the specific heat of the air), and if we compare it with 

 the formula of La Place, a difference will be perceived between the two in the 

 length of space, which a sound-wave is computed to traverse in a second. This 



