FOG CHAMBERS. 



49 



43. Notation. As above, the angular diameters, <, of coronas will 

 be given in terms of s, where 3oXsin </2 = .y/2, as the arms of the 

 goniometer are 30 cm. long ; usually ^ = 5/30, nearly. To secure 

 clearer vision, the goniometer was moved up to the plate-glass window, 

 placing the eye somewhat over 30 cm. off. The source of light, how- 

 ever, was left at 250 cm. from the trough, as above, and a correction 

 applied for the distances. 



M- 



44 



43 



FIG. 43. Rectangular fog chamber A, with lead tube T, filter pipe F, and exhaust 



pipe E. 

 FIG. 44. Cylindrical fog chamber A, with lead tube P, exhaust pipe E, filter pipe F, 



and plug/. 



In the tables, n usually denotes the number of nuclei per cubic 

 centimeter of the exhausted air, A*" the number per cubic centimeter of 

 the air at normal pressure and temperature. In successive exhaus- 

 tions, without fresh nucleation, the apertures will be written s ^ s% s 3 



and the nucleations corresponding Nt N z N 3 If, however, 



fresh nuclei are added, or if the exposure to the radiation is con- 

 tinuous, si Si' s"' and AY AY' AY" are usually used. The difference 

 of pressure in centimeters of mercury between the inside and the out- 

 side of the fog chamber (taken at 76 cm.) is denoted by 8/>. Hence 

 if p' is the vapor pressure of water vapor, the corresponding volume 

 expansion is (76 />') / (76 p' ^p}. D denotes the distance of the 

 source of radiations (X-ray bulb, etc.) from the end of the fog chamber 

 nearest it. 8/> usually refers to the fog limit, i. e., the pressure 

 difference, below which there is no condensation in saturated dust- 

 free air, within the scope of measurements made by aid of coronas. L 

 shows the time elapsed between the end of the exposure to radiation 

 and the condensation. 



EFFECT OF LARGE PRESSURE DIFFERENCES. 



44. Nuclei in dust-free air not energized. In table 29 periodicity has 

 been all but wiped out, and the incoming and outgoing series lie as 

 nearly on a curve as may be expected. 



