410 Proceedings of Royal Society of Edinburgh. [sess. 
sufficiently as to what would happen had we shone the rays on an 
insulated metal surrounded hy an absolutely identical metallic 
surface connected to sheaths. Another experiment towards 
answering this question will he described in a later part of our 
paper. 
The preceding results of the action of Rontgen rays are very 
similar to, and wholly in accordance with, the results found hy Mr 
Erskine Murray, and described hy him in a communication to the 
Royal Society of London, March 19, 1896. 
§ 19. They are analogous to those found for ultra-violet light hy 
Righi {Rend. R. Acc. dei Lincei , 1888, 1889); Hallwachs (Wiede- 
mann's Annalen , 34, 1888); Elster and Geitel (Wiedemann's 
Annalen , 38, 41, 1888); Branly ( Comptes rendus, 1888, 1890),. 
and others. 
We have also made some experiments with ultra-violet light, in 
which this similarity is further brought out. The method we have 
employed is that of Righi. 
A cage of brass wire gauze was made and connected to sheaths. 
Inside it the insulated metal was placed on a block of paraffin, and 
connected to the insulated terminal of the electrometer hy a thin 
copper wire protected against inductive effects. The light from an 
arc lamp was then shone through the gauze, so as to fall on the 
insulated metal perpendicular to its surface (see diagram 5). 
The experiments were of the same nature as those with the 
Rontgen rays, except that wire gauze letting through the ultra- 
violet light was substituted for the non-perforated aluminium 
cylinder transparent to the Rontgen rays. The insulated metal 
disc was 2 cms. distant from the gauze of brass wire. The steady 
