Spectra of Helium, Sfc. in the Ultra-Violet. 



305 



In concluding we wish to point out that this method can 

 be developed to exhibit considerably greater definition, so 

 that it promises to be useful in a variety of connexions. By 

 narrowiug the slits to *3 mm. the spectrum can be explored 



Fig. 9. — Mercury and Hydrogen High Pressures. 



-2 -4- -6 -8 1-0 1*2 1*4. S-6 1*8 2-0 2-2 2-4 



<- Amperes 



Scale for X and v as for fig. 6. 



in the region between A, 600 and A. 100 in steps of the order 

 of 25 wave-lengths (or better, depending on the field current 

 adjustment). The use of an electrometer with a sensibility 

 of 25,000 volts per division ought to make the use of such 

 narrow slits possible. The present experiments are thought 

 to be accurate and dependable between the limits indicated 



