no vnunw IN BARiriED OASES 



Since iwything i ymraetrical about the axis, if we write r for z' + y' 

 we find at the solution of this equation 



m A4- ^r* ..(73). 



If Q denotes the quantity of gas which passes through a section of the 

 tube in unit of time 



At the inner surface of the tube we have r-a, and 



1 dp , 

 = A + ^~dz a 



JL+-L4* ..(75) 



vpa* * 8/1 dz 



dw 1 dp 

 d^-^dz" 



The last of equations (71) may therefore be written 



- ................... (77). 



8/1 v ' dz p0 dz 



Equation (77) gives the relation between the quantity of gas which passes 

 through any section of the tube, the rate of variation of pressure, and the 

 rate of variation of temperature in passing along the axis of the tube. 



If the pressure is uniform there will be a flow of gas from the colder to 

 the hotter end of the tube, and if there is no flow of gas the pressure will 

 from the colder to the hotter end of the tube. 



These effects of the variation of temperature in a tube have been pointed 

 out by Professor Osborne Reynolds as a result of the Kinetic Theory of Gases, 

 and have received from him the name of Thermal Transpiration : a name in 

 strict analogy with the use of the word Transpiration by Graham. 



But the phenomenon actually observed by Professor Reynolds in his ex- 

 periments was the passage of gas through a porous plate, not through a 

 capillary tube ; and the passage of gases through porous plates, as was shown 



