1490 



Journal of Applied Microscopy 



line D, falling oft" abruptly on either end, and only slightly sensitive to the 

 greens and blues. 



Group II — Characterized by two distinct maxima — one a little above the 



Fig. 1. 



Apparatus for making spectrograplis. A. Spectroscope. B. Back of camera, carrying screen and plate- 

 holder. C. Supports upon which the back (B) may be moved. D. Shutter. 

 K. Color screen in color screen holder. 



D line, and the other in the blue-green, 

 sensitiveness falls very considerably. 



Fig. 2. 



Kxplanation to Figure. — The upper curve shows the visual in- 

 tensity of the spectrum (from Fraunhofer). Curves I-V repre- 

 sent the photographic intensity of the sjjectrum taken on plates 

 from group of corresponding number. C.koi'f 1 — Cranur 

 isochromatic (slow). Gkoi'p II — Standard orthochromatic 

 (slow) ; Forbes orthochromatic (slow) ; Carbutt orthochro- 

 matic (slow); Otto Perutz. (Skoif 111 — I.ovell color-dif- 

 ferentiating; American spectrum plate. CIkoip IV — Cadett 

 !<; Neal spectrum plate (slow). CiKoif V — International 

 " F.rethro." 



Between these two maxima the 



Group III — ^Characterized by 

 having its maximum sensitiveness 

 in the blue (as with ordinary 

 plates), with lesser bands of sen- 

 sitiveness extending below the D 

 line. 



Group IV — Characterized by 

 bands of sensitiveness extending 

 below line D, with greatest inten- 

 sity in the yellow-green, and fall- 

 ing off at the violet end before 

 H,. 



Group V — This group most 

 nearly approaches perfection. It 

 is characterized by a sensitive 

 band well below line D, and 

 somewhat below the red end of 

 Groups III and IV. This plate 

 gives an almost uniform degree 

 of sensitiveness with a maximum 

 intensity in the green. 



If sensitiveness to the spec- 



