1904.] Atmospherical Radio-activity in High Latitudes. 209* 



" Atmospherical Radio-activity in High Latitudes." By Geoege 

 C. Simpson, B.Sc,, 1851 Exhibition Scholar, Owens College,. 

 Manchester. Communicated by Arthur Schuster, F.RS. 

 Received February 3, — Bead February 18th, 1904 



In 1901 Elster and Geitel first showed that a wire stretched out in the 

 open air and charged to a high negative potential becomes radio-active ; 

 this observation has since been repeated by others, and the discoverers 

 themselves have undertaken a series of daily measurements extending 

 from December, 1901 to December, 1902. As the geographical distri- 

 bution of the atmospheric radio-activity is at present entirely unknown,, 

 the observations which I have been able to make here in Karasjoh 

 (Norway, 69° 20' N., 25° 30' E.), by the courtesy of the Commissioners 

 for the 1851 Exhibition Scholarship, must be of considerable interest. 



In my measurements I have used the method described by Elster 

 and Geitel in the ' Physikalische Zeitschrift.'* A wire was stretched 

 between an insulator in the open and another in my living room, the 

 part exposed to the open air, ] metres long, could be detached from 

 the rest. The wire was charged to a negative potential by means of a 

 small influence machine, built on the principle of a Kelvin replenisher 

 and driven by a weight : by means of a variable high resistance, con- 

 sisting of a strip of ebonite, one side of which had been rubbed with a 

 black-lead pencil and so mounted in a tube that an earth-connected 

 pad could move along it, the potential of the wire could be very easily 

 regulated. In all my observations the potential was maintained at 

 about 2250 volts, never rising above 2500 and never falling below 

 2000. The wire after being charged for 2 hours was removed to have 

 its radio-activity determined ; this was done by wrapping it round a 

 cylinder of wire netting which fits inside the "protection cylinder" of 

 an Elster and Geitel dissipation electrometer, which for this special 

 purpose is closed at the bottom as well as the top ; the rate at which 

 the electrometer is discharged gives a measure of the induced radio- 

 activity. Elster and Geitel have chosen the following as the arbitrary 

 unit of the induced radio-activity. " The activity of the air is put 

 equal to 1 when, after a 2 hours' exposure, a metre of the wire reduces 

 the potential of the dissipation cylinder by 1 volt in 1 hour." The 

 radio-activity when expressed in this unit is denoted by A in the 

 accompanying tables. 



The mean value of the radio-activity at Wolfenbiittel in mid- 

 Germany, as determined by Elster and Geitel during the year 1902, was 

 18'6, the individual values varying between 6-4 and 4. A complete 

 discussion of the effect of the different meteorological elements is given 

 in the original paper, f 



* Vol. 3, p. 305, 1902. 



f ' Fhysilalische Zeitsebrift,' vol. 4, p. 526, 1S03. 



