779 
tube; Z is the sliding holder for the dark slide (5,2 by 8,4 cm) and can be 
raised by means of a vertical screw (not shown) of 1 mm. pitch. The drums were 
slitted in such a way that only a strip of the sensitive plate 30 mm. long and 
ATI 
3 mm. broad was illuminated at each exposure. The double spectrum formed was 
about 15 mm. broad and was 25 mm. long for the range 4358 A.U. to 2805 A.U. 
Nineteen photographs could be taken one below the other on a plate 4.5 cm. by 
6 cm. (Lumière Agfa-plates specially sensitive to extreme ultraviolet). The exposures 
