162 Intelligence and Miscellaneous Articles. 



from radiant heat, all motion would cease ; for experiment tells 

 us that it is only when at or about the freezing-point that 

 ice is what Principal Forbes called viscous. It is interesting 

 to note that those particles of ice which have to carry the 

 greatest load, that is, are in a state of compression, are the 

 most likely to be the first melted; a fact which not only ac- 

 counts for the inability of ice to extend much when in tension, 

 but increases the efficacy of liquefaction and recongelation to 

 produce glacier-motion. 



I will not attempt to refer to the bearing of this theory 

 upon ribboned structure and the many other interesting 

 peculiarities of glacier ice, the present opportunity not being 

 convenient for their detailed treatment. 



XVII. Intelligence and Miscellaneous Articles. 



ON THE INFLUENCE OF LIGHT UPON THE ELECTRIC DISCHARGE. 

 BY E. WIEDEMANN AND H. EBEKT. 



pEOF. II. HERTZ * in a recent paper, " On the Influence of 

 -*- Ultra- Violet Light upon the Electric Discharge,'' has described 

 a series of experiments which show that light-rays, and, according 

 to Prof Hei'tz, exclusively the extreme ultra-violet rays, exert 

 a certain influence upon the passage of electricity in a spark- 

 discharge. It remained uncertain whether this iufluence was of a 

 primary nature, or whether the passage of the discharges was 

 effected by secondary impulses produced by the action of the light. 

 In order to obtain a nearer insight into the conditions and nature 

 of the phenomenon, we have, in the first place, repeated Hertz's 

 experiment, and always with complete success ; then we have 

 further varied the conditions of the experiment, and have thus 

 obtained the following results. As source of light we nearly 

 always employed an electric arc-lamp ; in particular cases burning 

 magnesium. 



(1) The phenomenon is seen with the greatest regularitv not 

 only with the discharge of an induction-coil, but also when a Holts 

 machine is used, that is, with statical electricity, if the discharge 

 upon which the light acts is contained in a secondary circuit of a 

 Holtz machine, the spark-length of the primary circuit being varied 

 by means of a spark-micrometer. Illumination of the discbarge 

 produces a lowering of the potential necessary for the passage of 

 the electricity. 



(2) In order to study the influence of the light during the 

 passage of electricity in the passive discbarge, one pole of t he machine 

 was connected with the earth ; the electricity accumulated upon the 



VTierl. Ann. xxxi. p. 983 (1887). 



