Dike — Recent Observations in Atmospheric Electricity. 199 



may be further analyzed into higher frequencies of the order 

 of 1,000,000 cycles per second by coil resonators arranged to 

 affect strips of sensitive paper by their brush discharge when 

 excited by frequencies of the proper pitch. The potentials were 

 approximately measured by graduated needle gaps, a number of 

 which were arranged in parallel rows, with fuses and high 

 resistance in series, the potential falling between the minimum 

 sparking pressure of the longest gap crossed and that of the 

 next higher. The measurement of the lightning current was 

 difficult, as it depends on the capacity, inductance and resist- 

 ance of the lines and the frequency of discharge. The 

 quantity of the discharge over the line was estimated by not- 

 ing the size of fuse that it would just burn out, several fuse 

 wires of different sizes being placed in series, the arc holding 

 in the vapor of the first fuses blown till the larger ones were 

 melted. Using the data from one of these tests, the quantity 

 of discharge was estimated at 0*003 of a coulomb, and if this 

 quantity of electricity was spread out over a mile of wire 

 having a capacity between line and ground of 0*01 micro-farad 

 the initially impressed voltage would be about 600,000 volts. 



The development of the theory of the ionization of gases 

 opened up a new field of investigation in Atmospheric Elec- 

 tricity, since it afforded an explanation of the previously 

 observed fact, that a charged body exposed to the air lost its 

 charge at a more rapid rate than could be explained by leak- 

 age over the insulating supports. Elster and Geitel were pion- 

 eers in this field, and though the instruments devised by them 

 for observing the "dispersion" gave erroneous results through 

 the establishment of saturation currents, that is, currents inde- 

 pendent of the potential difference, once a certain minimum 

 potential is passed, they accumulated much information of a 

 relative nature. It is to J. J. Thomson and his school that 

 we are indebted for a better understanding of the conductivity 

 of gases, leading to the construction of apparatus on more 

 correct principles ; results are now being obtained which may 

 probably pretend to some degree of accuracy. The experimen- 

 ter in these lines must be satisfied with somewhat approximate 

 results, since it is obviously impossible to measure a con- 

 ductivity to one or two per cent when its value is varying dur- 

 ing the time of measurement by perhaps fifty per cent. The 

 order of magnitude can be arrived at, but the conductivity of 

 a gas is quite a different matter to that of a metal where the 

 number of ions seems to be infinite, and atmospheric air is even 

 more unstable in its properties than a confined sample of gas. 



The establishment of saturation currents in the apparatus for 

 determining the conductivity of the air may be prevented in 

 two wavs, either by the removal of all other conductors to such 



