STANDARDIZATION AND EFFICIENCY OF THE FOG CHAMBER. 



35 



values of dp/p, it is nearly twice as efficient as No. i. What is particu- 

 larly interesting is the definite occurrence of coronas of the first order, viz: 

 the crimson c 1; and the red r t , above the green g 2 . The observer is left 

 in doubt as to this, unless correlative measurements of aperture are made, 

 which in case of table 13 was not feasible for so small apparatus. Such 

 results are given, however, in table 14. 



TABLE 13. Comparison of large and small fog chambers. Dust-free air. Fog chamber 

 No. 2, length 1 10 cm., diameter 14 to 22 cm. ; fog chamber No. 3, length 16 cm., diam- 

 eter 1 1 cm. 



All fog chambers which have aged are free from internal sources of 

 nuclei, whereas when freshly installed they may generate them through- 

 out many successive exhaustions. Even after this, production of nuclei 

 is still appreciable if long intervals of time elapse between the exhaustions. 

 An endeavor was made to detect the nature of this phenomenon, but a 

 satisfactory answer has not yet been reached beyond the surmise given 

 above. The production is observed both in large and in small chambers 

 and the nuclei are dust-like in size. 



