1288 



neighbourhood of P proxies that no fibres will be seen with honio- 

 geneous light and that those observed with non-homogeneous light 

 are only due to the spectral shift considered in § 7. It is namely 

 evident, that a line at P directed along CP which existed already 

 with monochromatic ligiit, could never be reduced to a [)oint by 

 means of a prism. 



Finally we must remark the following. At great distances from 

 P it is no longer true that the fibres are directed along radii with 

 ƒ* as a centre. In reality the lines along which the fibres are directed 

 have approximately the course indicated in the figure by J^L'. To 

 explain this we should have to enter into too many details. 



