348 Prof. Apjohn on the Specific Heats of the Gases, 



of mobility in question have any influence if the gases be all 

 made to move over the thermometers with the same velocity ? 

 If indeed a wet thermometer were to be immersed in atmo- 

 spheres of the different gases either absolutely dry, or in the 

 same hygrometrical state, the depression might be expected 

 to be greatest in those whose molecules were most mobile. 

 But it appears to me very obvious that in the methods of ex- 

 perimenting adopted by M. Suerman, as all the gases, after 

 contact with the wet thermometer, are by the mechanical 

 means employed removed with the same degree of speed, 

 the reduction of temperature experienced by this instrument 

 must in every instance be altogether independent of any pecu- 

 liarity in the constitution of the respective gases, in virtue 

 of which heat may be propagated through some with greater 

 facility than through others. But it is not necessary to insist 

 further on this point, for M. Suerman materially modifies the 

 opinion previously expressed by him, as will be seen by the 

 following extract from page 90 of his Thesis : " Corrigitur 

 quidem pro maxima parte hie effectus aucta motus celeri- 

 tate, num vero omnino ita tollatur, satis certo affirmari non 

 potest." 



But there is another position of M. Suerman's which ap- 

 pears to me more untenable still. In his experiments all the 

 gases were driven over the thermometers with the same ve- 

 locity, so that the quantities by weight which passed them 

 in a given time were necessarily proportional to their specific 

 gravities. Now in reference to this circumstance Suerman 

 has the following passage : *' Relativus autem radiationis ex 

 cylindro continenti effectus hinc pendere debet. Qui, ut 

 idem esset, celeritas motus in diversis fluidis elasticis ita fuisset 

 modificanda, ut, cseteris paribus, rationem inversam servaret 

 ponderum specificorum." Here an influence is ascribed to mass 

 which I cannot comprehend, for it is asserted that the relative 

 effect of radiation is not the same for all the gases, unless the 

 same ponderable amount of each passes in a given time over 

 the wet thermometer. The very opposite of this proposition 

 appears to me to be the truth. We have already seen that 

 the ratio borne by the caloric which radiates from the sides 

 of the tube to that extricated from the air cooled by contact 

 with the moistened bulb, diminishes as the velocity of the 

 current increases. Surely then, in order that this ratio be 

 the same for the different gases, they must be all made to 

 move with the same degree of speed. I do not, in fact, see 

 what we have at all to do with the consideration of mass, and 

 its introduction appears to me only calculated to confuse and 

 mislead. 



