12 k 2 



Mr. A. Griffiths on Diffusive Convection. 459 



This is a forcible illustration of the necessity for complete rest 

 in diffusion experiments. 



What is of chief importance here, however, is not the error 

 produced in one tube, but the resultant error due to the 

 flow in the two tubes. 



The quantity transmitted along the two tubes is 



t-AT t-AT 



_»Li v~L 2 



l—e~k l — e~k 

 kAT/. 1 vL, 1 v 2 L, 2 \ &AT/ 1 vL 2 



*AT/ 1 v*W\ *AT/ 1 ^L 2 2 \ 

 ~ L : \ + 12 F J 1 L 3 V + 12 A: 2 )' 



1 w 2 L 2 

 The correcting factor equals 1 + ys —p^ approximately; or, 



substituting the value obtained for ?;, 1+ t ( y— ). Sub- 

 stituting the values given above for SL and L ls the value 

 obtained for the correcting factor is 1*00012 approximately ; 

 or the error due to the convection- current equals about one- 

 hundredth of a per cent. 



Section V. 

 Tubes of unequal bore. 



Let A = sectional area of the longer tube of length L x and 



r 2 A = sectional area of the shorter tube of length L 2 . 

 Let v = velocity of flow in the shorter tube, then 

 r 2 v= velocity of flow in the longer tube. 

 By algebraical considerations similar to those already em- 

 ployed it can be shown that 



6JcSL 



6kr 2 BL 



When r 2 =0, the velocity in the shorter tube equals -f-y» 

 whilst the velocity in the longer tube is zero. 2 



When r 2 = co , the velocity in the shorter tube is zero, and 



the velocity in the longer tube is T 2 . 



The maximum value of the velocity along a tube occurs 

 when its bore is infinitely small in comparison with that of 



r 2 v=. 



