Mr. A. Griffiths on Diffusive Convection. 

 Putting Y X =:Y 2 . we obtain 



463 





This is the same result as that obtained in Section III., 

 when viscosity was neglected. 



Section VII. 



An Experimental Illustration of Diffusive Velocity. 



The adjoining figure is a diagrammatic sketch of an 

 apparatus kindly made by Mr. F. W. Rixon to test the 

 existence of diffusive convection. 



Fig. 5. 



¥ 



=ZE--^& 



The upper extremities of two tubes, A and B, of equal 

 diameter but slightly unequal in length, terminate in com- 

 partments connected by a capillary tube CD. 



Any motion down B and up A is magnified in the pro- 

 portion of the sectional area of A or B to the sectional area 

 of the capillary tube. 



The motion along CD is detected by the addition of 

 copying-ink or other colouring matter. To introduce the 

 ink, the taps E and H are closed, G and F opened, and the 

 ink poured down F. 



Owing to viscosity the velocity of the liquid at the centre 

 is double the average velocity. 



In the experiments, the results of which are recorded 

 below, the tubes A, B, &c. were filled with water and placed 

 in a strong solution of copper sulphate, the taps E_, F, G, 



2K2 



