the Flow of Gases. 197 



of gas discharged owing to the great effect of slight varia- 

 tions of temperature on the relations between changes of 

 pressure and changes of temperature, such changes of tem- 

 perature being almost necessarily incidental on changes of 

 pressure. 



11. In Mr. Wilde's experiments the pressure was allowed 

 to fall in the discharging vessel during the discharges ; this 

 would cause a corresponding fall of temperature, which 

 would again cause heat to flow from the metal vessel into the 

 gas within. 



It is difficult therefore to say what the change of tempe- 

 rature was except in the extreme cases. With the experi- 

 ments on the highest pressure, however, the times 7*5 

 seconds, and the greatest possible falls of temperature 5°*5, 

 were so small that the communication of heat from the walls 

 of the receiver would have been very slight ; and hence we 

 might expect that the discharges, calculated on the assump- 

 tion of no communication of heat, would agree with the 

 theoretical discharges multiplied by the real coefficient of 

 contraction. This would be shown by an agreement in 

 the successive coefficients obtained from the experiments 

 with the higher pressures. On the other hand, with the 

 lowest pressures the times were so considerable, 170 seconds, 

 and the greatest possible falls of temperature (assuming no 

 conduction, 94°) so great, that the communication of heat 

 would have been very great and, considering the compara- 

 tively small mass to be heated (only one thirteenth of what 

 it is in the highest experiments), might maintain the tempe- 

 rature approximately constant after falling some considerable 

 amount below the initial temperature. In these last experi- 

 ments, therefore, it would be expected that the discharge 

 might be estimated as taking place at nearly constant 

 temperature. 



The intermediate experiments would give intermediate 

 results. 



According to this view, for the high pressures, since 



H9=(0 n > w 



and &--71*, (20) 



Pi Px 



or putting V for the volume 573 cub. in. of the discharging 

 vessel, 



$'•"&, (2D 



Phil. Mag. S. 5. Vol. 21. No. -130. March 1886. P 



