345 



of the components of our pair of limb-lines 





(19) 



^ 8. The difference in mutual influence of dijfusion lines at the 

 limb and in the centre of the disk. 



In conformity with our procedure with the refraction lines, we 

 are now going to determine also in the case of pnre diffusion lines 

 an upper limit for the apparent displacements which the components 

 of a pair impart to each other. We therefore consider the point 

 Ml midway between the Z-boundaries of one of the lines, defined 

 by tlie absciss 



lM=fAiR +h) 

 and will only have to compute how much this value differs from 

 ± A. But we are especially interested in the difference between the 

 apparent displacements of a component in the limb-spectrnm and of 

 the same line in the centre-spectrum, i.e. in the quantity 



1'm-Im = '/AI-'r +1'v-Ir-Iv). 

 for which we find, after substituting (18) and (19), 



B \ / B^ A' B' \ / A' B" 

 ' " 4 1 1^ B' B' B y B' B' 



I yW' A^ B'l / 7} ^' 



-f / h4 \/ 16— H 



y B^ B^ bV B* B^ 



-1/ 1 + 41 + 1/16^+1- 



(20) 



The numerical value of this expression has been calculated for 

 four different widths of the lines, namely B = 0,050, 0,070, 0,100 



and 0,200 A. We took B' always to be =^ + 0,010 A, and 



2A 

 selected a number of distances A so as to have values of -jr- (as 



abscisses) suitably situated for plotting curves. 



The dotted curves in Fig. 7 show the result. All ordinates should 

 be imagined negative, because in this case there pi'oves to be an 

 apparent attraction of the components. We notice that the effect is 



