﻿34 



Dr. H. Stansfield and Mr. H. P. 



Walmsley on 



two neighbouring primary maxima there are six secondaries, 

 which all show clearly in the first order left and right in the 

 original negative. As there is in this case no aberration, the 

 secondaries are symmetrical on the two sides of the central 

 primary maximum. 



To produce aberration we made use o£ Lord Rayleigh's 

 suggestion of employing the cubic curve associated with a 

 bent plate*. A bent sheet of mica formed one side of a cell 

 which was filled with ether vapour. In fig. 3 a section of 



Fisr. 3. 



> 







oitb 





v 







J/^^r — _ ' \r-Mlca. 



■■:.:■.: .•■/•:•: -V////////////. 





mmmmmimim 



QU 



.ss plate 



Small 



' Sec °*d*rc es 



7 



-- trafli* 5 



tte^ 



VJavt' 



Larg e 



Seeo "darU s ' 





Section of Aberration Cell and Diagram of Changes produced 

 in a Wave-front passing through it. 



the cell is drawn together with a diagrammatic indication of 

 the changes in direction and form produced in a wave-front 

 passing through it. 



* Ravleigh, Coll. Works, vol. iii. p. 59, note. Phil. Mag. vol. xv. 

 p. 554 (1908). 



