58 Notices respecting New Books. 



comparison of air-thermometers charged with air under an initial 

 pressure of 762, 553, and 438 millims. In a subsequent series 

 of experiments, the initial elastic force of the air was carried as far 

 as 1486 millims. The experiments were made from 0° up to 

 325° of the scale made with the graduation of the instruments be- 

 tween 0° and 100°. All these thermometers proceeded in sensible 

 agreement, even when the air which each contained was under very 

 different pressure, so that it may be admitted with all certainty, thai 

 the air-thermometer is a perfectly comparable instrument, even when 

 charged with air of different densities. 



Two thermometers charged, one with air, the other with hydro- 

 gen, with an initial elastic force of 754 millims. at 0°, proceeded 

 with perfect agreement from 0° to 325°. The same was the case 

 with two thermometers of carbonic acid gas, which, in two series of 

 experiments, proceeded in equally perfect agreement with the air- 

 thermometer. The last was in both cases charged with air of an 

 initial elastic force of 742 millims., while in the carbonic acid gas 

 thermometers the initial elastic force of the gas was, in one 741 

 millims., and in the other only 464 millims. It must be observed 

 that the temperatures were calculated, in the various experiments, 

 by taking for the coefficient of dilatation of air 0*003665, for that 

 of hydrogen 0-003652, and for that of carbonic acid 003695 when 

 it was under the pressure of 741 millims., and 0'03682 when it was 

 under the pressure of 464 millims. 



Two series of experiments made on the comparison of a normal 

 air- thermometer with a thermometer of sulphurous acid gas, under 

 the initial pressure of 762'17 millims. for the air, and successively 

 of 751*47 millims. and of 588*70 millims. for the sulphurous acid, 

 showed a very notable difference of course between the two instru- 

 ments. In the first series 0003825 was taken for the coefficient of 

 dilatation of the sulphurous acid gas, and in the second 0'003794. 

 The sulphurous acid thermometer fell behind the air-thermometer 

 from the point of 100°, and the differences increased regularly with 

 the temperature. Thus the mean coefficient of dilatation of sul- 

 phurous acid gas diminishes in a very marked manner with the tem- 

 perature measured in the air-thermometer ; in fact, the value of this 

 mean coefficient for each degree Centigrade is found to be 



fromO to 98° 12 0*0038251 



... to 257-17 0*0037923 



... to 310*31 0*0037893' 



The Mercurial Thermometer. 



' The air-thermometer is the only instrument, especially for ele- 

 vated temperatures, which can be used in exact experiments, but 

 the use of it is difficult ; there are even circumstances in which it 

 is impossible to employ it. Then it becomes necessary to use a 

 mercurial thermometer ; and then a direct comparison must be made 

 of this instrument with the air-thermometer, in order that its indi- 

 cations may be transformed into those of the normal thermometer. 



