NEW SPECIES OF "N RAYS 69 



exploring this region, by means of a narrow slit 

 filled with phosphorescent calcium sulphide, I 

 ascertained, without any difficulty, that, in 

 certain azimuths, the glow of the spark 

 diminished under the action of the rays, and 

 increased, on the contrary, when they were 

 intercepted by a wet screen. These were, in 

 fact, the looked-for radiations ; I will call 

 them " NX " rays. 



Although the aluminium prism of 27 15' I 

 used previously is suitable for these experi- 

 ments, nevertheless, in order to increase the 

 dispersion, I used an aluminium prism of 60, 

 and afterwards another of 90. With the help 

 of the latter, I very carefully studied the feebly 

 deviated part of the spectrum. The prism was 

 arranged so that the angle of incidence was 20 ; 

 for each radiation, the deviation was measured 

 and the refractive index deduced ; then the 

 wave-length was determined by means of a 

 Brunner grating of 200 lines to the millimetre, 

 by the process already described (see p. 57). 

 The following table gives the numbers which 

 result from this study, and were used for 

 constructing the diagram (Fig. 10), in which 



