Proceedings. 3 



glacier which stretches down from the Dent Blanche towards 

 Ferpecle, and there noticed a phenomenon which has probably- 

 been described before, although I cannot recollect any 

 definite reference to it. The sky was perfectly clear, but a 

 cloud filled the valley of Evolena, and reached up to a 

 height of about 7,000 feet, while I was at an altitude of 

 about 1 1,000. About once every two or three minutes there 

 was an electric discharge, of the kind known as sheet light- 

 ning, from the cloud upwards. At the time, I was under 

 the impression that the discharge took place between the 

 cloud and the rocks of the Dent Blanche ; but, on considera- 

 tion, it seems to me equally probable that the discharge took 

 place towards the upper parts of the atmosphere. The 

 following reflections are suggested by the phenomenon : — 

 The cloud lay in a deep-cut valley, the mountains on all 

 sides rising high above it. If the cloud was at the same 

 electric potential as the surrounding parts of the earth, there 

 could be no discharge between them, and we should certainly 

 not expect a discharge towards the upper regions of the 

 atmosphere to take place from the inside of a cavity. The 

 cloud therefore must have been at a different potential from 

 the mountains ; but unless there was some cause at work 

 which kept up that difference of potential we could not 

 have such a series of flashes lasting certainly for more than 

 an hour. The cloud seemed to rise up in the valley as time 

 went on, but probably the lower boundary kept stationary, 

 while the upper boundary of the cloud extended more and 

 more upwards as the mountain sides grew colder. If the 

 water-drops were charged electrically, and increased in size, 

 this would of course account for a gradual rise in potential. 

 We know too little, however, of what happens when a cloud 

 forms in an electric field, to speculate further." 



The following note on " Halos as Prognostics of Bad 

 Weather " was read by the author, Professor ARTHUR 

 Schuster, F.R.S. :— 



