790 



Prof. Townsend and Mr. Edmunds on the 



in a marked degree and also lending itself to mathematical 

 treatment. Some preliminany investigations were made by 

 Bailie and Graugain, but the latest and most complete sets 

 of measurements are those of Watson*, who investigated dis- 

 charges through air at pressures varying from one atmosphere 

 to half an atmosphere and with wires between 12*8 and *7 

 millimetres diameter. 



It was found f that an explanation of Watson's results 

 could be obtained on the hypothesis that the ionization was 

 due to collision, as had previously been found for discharges 

 between parallel plates at low pressures. The present inves- 

 tigation was undertaken to test the theory over a range of 

 pressures of air from one millimetre to 760 mm. with wires 

 of various diameters. 



2. For this purpose two cylinders of brass were used ; 

 a large one, internal diameter 14*9 cm. and effective length 

 66 cm., and a smaller one, internal diameter 3' 9 6 cm. and 

 length 44 cm. These cylinders were fitted with outlet and 

 inlet tubes in the sides for exhausting and admitting air, 

 and the ends were closed by thick glass disks through the 

 centres of which wires of various diameters could be inserted 

 and fixed. The free ends of the wires were enclosed in 

 sealed glass tubes, and the ends connected to the instruments 

 were shielded for some six inches by glass tubes and the 



Fig. 1. 



POMP AND GU/ICE 



Dftr/A'C TUBES. 



rest by rubber tubing. The arrangement of the apparatus 

 is shown in the accompanying diagram, figure 1. 



* E. A. Watson, ' The Electrician,' Feb. lltli, 1910. 

 t See ' Electrician,' June 6th, 1913. 



