MAGNUSSON — ANOMALOUS DISPERSION OP CYANIN. 



257 



special care and the results for solid cyanin films given in his 

 last 1 paper are shown in Table VI. 



Table VI. 



Pfliiger made an elaborate comparison of these data with the 

 values calculated by the Ketteler-Helmholtz dispersion formula. 



To overcome the difficulties of making prisms by Pfliiger's 

 method and in hopes of securing better results R. W. Wood 2 dis- 

 solved the dye in Canada balsam and poured the solution while 

 hot into the V shaped opening between two glass plates. Al- 

 though the prisms thus made were superior to those obtained by 

 Pfliiger, the dye was still in solution and the same objection 

 could be made as for dyes in alcoholic solution. He next tried 

 to fuse several of the aniline dyes and found that with cyanin 

 this was a singular success. While in a fluid state the cyanin 

 was pressed into an acute prism between two pieces of plate 

 glass. After cooling, one of the plates was removed by a sharp 

 blow, the prism remaining fixed on the other. The advantages 

 of this method are several : 



1st, The rapidity and comparative ease of making good prisms. 



2nd. The increased accuracy of the measurement of the re- 

 fracting angle which the superiority of the optical surface 

 makes possible. 



3rd. The improved definition of the transmitted beam on ac- 

 count of the uniformity of the prism. 



4th. The ability to obtain prisms of almost any desired angle. 

 Pfliiger considers an angle of 2' 6."4 remarkably large 

 while by this method prisms have been made with a re- 

 fracting angle of 2° and over and no special difficulty 

 would be met if larger angles were desired. 



1 Pfliiger, Wied. Ann. LXV., p. 227. 



s Wood, Phil. Mag. XLVL, p. 380, (1898). 



