224 



DR. W. GEOFFREY DUFFIELD ON THE 



TABLE VI. (continued). 



(7) Relation betiveen the Pressure and the Displacement. That the relation between 

 the pressure and displacement is approximately a linear one is evident from 

 Diagram 1, in which these two quantities are plotted. But the displacements per 

 atmosphere are almost invariably greater at low pressures than at high ones 

 (see Table III.) which seriously challenges the existence of an exact linear relationship. 

 This is clearly brought out by Diagram 2, in which the mean displacement per 

 atmosphere form the ordinates and the pressure the abscissae of the curves, each oi 

 which represents the behaviour of one particular spectrum line whose identity can be 

 traced from the number assigned to it. There is a general downward trend as the 

 pressure increases, which is in favour of the rate of displacement decreasing with 

 increase of pressure. This tendency is apparent in each of the two groups into which 



