﻿6 MORRIS-AIREY, Determination of Wave-lengths. 



air. Another adjustment which was found very neces- 

 sary, viz., inclining the plate to counteract the aberration 

 of the lenses for different wave-lengths, could also be 

 carried out in vacuo. 



These adjustments were, however, practically a source 

 of weakness to the instrument, as they involved the 

 perfect fitting of over thirty ground surfaces to maintain 

 the vacuum. 



A sudden rise or fall in the temperature of the 

 laboratory frequently involved taking the whole instru- 

 ment to pieces for relubrication of the sliding surfaces 

 before the apparatus could be exhausted. 



Using the discharge from a Leyden jar charged by the 



15 inch induction coil, I was able to photograph a group of 





 lines lying well beyond 1,852 A. 



To obtain a more powerful source of light, the electric 

 arc between two iron rods in vacuo was produced directly 

 in front of the slit. However, intense as the radiation 

 was in the ordinary ultra-violet, nothing could be detected 

 beyond 1,852. 



Vacuum tubes were again tried, with little success, 

 and finally a very powerful induction coil, built by 

 Klingelfuess, of Basel, was placed at my disposal by 

 Professor Kayser. 



This coil, when fed with a current of 50 amperes 

 interrupted by the Wehnelt electrolytic interrupter, easily 

 gave a spark of 1 metre length and about 2 cms. thickness 

 in air. 



This spark was reduced by a large plate condenser 

 to about 1 J cms. length, and allowing this to glide across 

 the face of the fluorspar window in front of the slit, so 

 as to reduce the air gap to a minimum, I finally succeeded 

 in obtaining lines in the aluminium spectrum extending 



o 



over nearly 200 A beyond the previous limit. 



