1090 



Mr. D. Coster on the Spectra of X-rays 



visible and the infra-red light at the same time. Hence a 

 blackening, which may be represented thus : I is regis- 



tered by the photometer thus : / \ *• 



Small irregularities of the plate which are not readily 

 noticed by the eye are registered by the photometer. Most 

 of the small abrupt changes of the curves must be explained 

 in this way. As a rule the more continuous changes corre- 

 spond to changes in the blackening of the plate. This may 

 be verified by comparing photometer-curves taken across the 

 plate at different heights. 



Fig. 1 gives a typical curve for Rh (taken in the opposite 



Fig. 1. 



Rhodium Lai with satellites (calcite crystal). 



direction as compared with the other curves). Fig. 2 shows 

 the great difference between the Rh t «i and the In u x line. 

 Fig. 3 clearly demonstrates that this difference suddenly 

 appears between Cd and Ag. (The numerous accidental 



* Another question is, whether the blackening of the plate really gives 

 a correct impression of the emission-spectrum. It might be supposed, 

 that for these strongly exposed lines the secondary radiation in the 

 photographic plate has some effect in broadening the lines, but as the 

 breadth of the lines largely depends on the space-lattice constant of 

 the analysing crystal (with gypsum rather sharp lines were obtained) 

 we may conclude that this influence cannot be very great. 



t This curve is taken at a height different from that in fig. 1. In 

 figs. 2, 3, and 4 Tn stands for In. 



