STANDARDIZATION OF FOG CHAMBER. 6l 



electrometer and fog chamber are of small importance. Ratios of 

 C' 10 = 86/17, 30/17, 20/17, and others, were tried. 



51. Method. In the preceding paper the value of e found was ulti- 

 mately dependent upon the velocity of the ions in the unit electric field. 

 In the present experiments a value will be found, based on the decay 

 constant 6= i.i X io~, of the ions. This method has the advantage that 

 large-core potentials are admissable in the electrical condenser, so that 

 an ordinary graduated Exner electroscope suffices for the measurement 

 of current. The small capacities of the instrument make it necessary to 

 insert an auxiliary condenser, as otherwise the discharges are too rapid 

 for trustworthiness. 



If a is the number of ions produced per second per cubic centimeter 

 by the radium within the condenser core, n the number of nuclei per 

 cubic centimeter in general, and N the number of nuclei (ions) found 

 when the core is free from charge, dn/dt = a w 2 ==o, if n = N. Again, if n 

 is the number of nuclei found when the core is charged and i the cor- 

 rected current observed, e Thomson's constant, and v the effective volume 

 of the fog-chamber condenser, 



(i) 



Hence if the capacity of the system is C and V, the corrected fall of 

 potential per second 



(2) 



Usually V is measured in volts, so that 1^/300 replaces V in the equation. 

 It is obvious that V must be large enough to keep the current V constant 

 and the observations always show this at once. 



If equation (i) is multiplied by throughout it will express the case 

 for the negative ions alone and the negative current alone. Hence 

 equation (2) is at once applicable here. 



52. Data disregarding external gamma rays. By the aluminum-foil 

 electroscope it was made convenient to use the high potentials of the 

 electric-lighting circuit (about 250 volts) for charging. 



The number of nuclei (ions) found in the presence of the radium tube- 

 lets and in the exhausted fog chamber free from charge at its central core 

 was ./V = 474, ooo. The number of nuclei found in the exhausted fog 

 chamber when the core was charged 250 volts was '==82,5oo. Hence 

 about 391,000 vanished in the presence of the electrical current, the 

 original apertures of the coronas being reduced from about 22 to 13. 

 The drop of pressure, dp/ ' = 0.30 nearly, was taken high enough to catch 

 all the available ions, but not so high as to catch the vapor nuclei of dust- 

 free wet air. 



