High Frequency Sjpectra. 



203 



A dividing engine, with a very accurate screw, was adapted for 

 measuring the distance between the lines. A vertical board was 

 carried by the moving platform of this engine. Two vertical 

 lines l.S.mm. apart were drawn on this board, and each line on 



w 



CX^Wa. 



WeWv 

















A increasincj 











Pu Pk 



Figure: 2. 



?\p P^Y 



the film was brought in turn exactly between these lines, and 

 the reading of the engine noted. Table I. shows a set of such 

 readings. 



Table I. (Distances in mm.). 



— 



w.«^. 



W.a, 



Pfc-aa. 



Pt.tti. 



W./3. 



W.y. 



Pt./3. 



Pt.y. 









113 



5-87 



7-10 



7-25 



8-51 



12-46 



13-66 









1-18 



5-84 



7U 



7-30 



8-48 



12-23 



13-46 









115 



5-90 



718 



7-29 



8-50 



12-38 



13-47 









1-14 



5-90 



710 



7-29 



8-42 



12-36 



13-41 









115 



5-88 



7-22 



7-33 



8-41 



12-29 



13.50 



Mean - 







115 



5-878 



7- 144 



7-296 



8-472 



12-34 



13-50 



It will be seen that, for the fainter lines, e.g., the p and y 

 lines of Ft., there is much greater variation in setting than for the 

 more intense lines. To evaluate the wave lengths the mean of 



10a 



