144 Intelligence and Miscellaneous Articles. 



emerging, the gas is led round the first tube to prevent any loss by- 

 radiation and conductibility ; and when the temperature has become 

 stationary, we may say that all the heat of the focus, which is known, 

 is taken by the gas, the temperature of which is increased by a mea- 

 sured quantity ; hence the specific heat can be deduced. 



There are two advantages in this method. The first is, that the 

 greatest cause of error which Delaroche and Berard, and afterwards 

 M. Regnault, met with is suppressed. In their experiments the gas 

 reached 100° in a calorimeter at 10°; and the greatest difficulty. was 

 felt in appreciating the heat which passes by conductibility from the 

 hot tube to the cold calorimeter. In my method the gas reaches at 

 the ordinary temperature (say, 10°), it passes from the spiral at 

 about 20° : the difference is 10° ; it was 90° before ; the present error 

 is at most one-ninth of the former. 



Here is the second improvement. The whole of my apparatus is 

 the size of a finger, it is of thin glass ; it might be of mica, even of 

 goldbeater's skin ; it weighs no more than a litre of gas, and expends 

 no more heat in reaching the final temperature. Ten litres of gas 

 are sufficient to make one measurement ; thus the difficulties which 

 for a long time had to be overcome in order to obtain a uniform cur- 

 rent disappear, ordinary gasometers suffice, and the method is appli- 

 cable even to vapours. A first determination gave the number 0*242 

 for air, instead of 0*237, which M. Regnault found. 



Thermometers, even, may be dispensed with, and the temperature 

 measured by the increase of resistance in the wires. It is known 

 that a resistance r at zero becomes r{\-\-a,t) at t degrees. That 

 being the case, let two equal bundles of wires be placed one after the 

 other in a tube ; then, having decomposed the total circuit into two 

 equal derived circuits, let us make each of them pass, first through 

 one of the two bundles of wires, then into a differential galvano- 

 meter ; the latter remains at zero. But if a current of gas at t degrees 

 be sent through this tube, it will pass at t-\-Q in the first spiral, at 

 t-\-2Q in the second; they take a difference of temperature 6, a 

 different resistance, and the galvanometer is deflected. It is reduced 

 to zero on introducing, by means of a special rheostat, a platinum 

 wire into one of the circuits. The length of this wire is proportional 

 to the increase of temperature d ; it admits of measurement. 



The same apparatus is applicable to vapours. The liquid to be 

 examined is distilled as regularly as possible ; the current of vapour 

 is at first superheated by the first bundle of wires, it afterwards tra- 

 verses the second, becomes heated by a quantity 6, which is measured 

 as before ; the vapour is condensed, and afterwards weighed. In order 

 to take into account the irregularities of the distillation, it is neces- 

 sary to observe the apparatus from minute to minute. 



III. Latent Heat. — In order to measure latent heats, a double 

 alembic is employed, of which one part is exterior ; the liquid in it 

 is caused to boil, and the vapour is brought there after having been 

 condensed by a refrigerator : the effect of this is simply to raise to 

 the boiling temperature the interior alembic, which contains the 

 same liquid, and in which is immersed the spiral, the resistance 



