38 VAPOR NUCLEI AND IONS. 



These results, together with the data of table 12, are shown in fig. 22. 

 For the air curve a marked advance beyond the results of table 1 2 is at 

 once apparent, but it is noteworthy that the slopes of both curves are in 

 the main the same, in spite of the fact that the former rises to but one- 

 half or one-third of the height of the new curve. The efficiency of both 

 fog chambers therefore terminates abruptly in a final or fixed corona or 

 (in the chart) in an asymptote which would be horizontal, if it were not 

 necessary to assume that the quantity of water, m, precipitated per cubic 

 centimeter increases with the drop in pressure. In the different series, 

 irregularities are often apparent which are difficult to explain, though at 

 low values they may be due to cosmical radiation. Thus the second 

 series for non-energized air rises more abruptly than the first and third, 

 results which are possibly associated with the presence of water nuclei 

 and referable to different degrees of leakage from fog chamber to vacuum 

 chamber; but it is also possible that unequally rapid closing of the stop- 

 cock after exhaustion may have left an impression. The results for 

 radium and the X-rays will reappear under better conditions presently, 

 and may then be discussed. One may note that for weak radiation the 

 graphs intersect the graph for non-energized air. 



38. Continued. Shorter pipes. The next step consisted in a remodel- 

 ing of the apparatus, whereby shorter connecting pipes would suffice. 

 Two 6-inch nipples, 1^ inches in diameter and containing a 2-inch plug 

 stopcock, now joined the fog and vacuum chambers. The results are 

 shown in table 14 and in fig. 23. The fact that the main resistance is still 

 encountered in the gas cock is proved by the need of stops to insure quick 

 and complete opening. Whenever the cock is nearly but not quite 

 opened, however suddenly, low coronas are observed. When this was 

 remedied, fixed coronas thereafter corresponded to each dp. The table 

 contains the usual series of comparative results for air energized by 

 radium and the X-rays. 



As compared with the preceding data there is a small shifting of the 

 graph toward lower pressures, while the slopes in the representative parts 

 of the curves are practically the same. The terminal corona, however, and 

 the corresponding asymptote, is markedly raised. Nevertheless, though 

 the large green-blue-purple corona now appears in the case of strongly 

 energized air, it has not yet been reached in the non-energized cases. 

 The limit of efficiency is therefore not yet in sight when a fog chamber of 

 about v = 6,000 c. cm. empties into a vacuum chamber of about V 

 100,000 c. cm. through 30 cm. of piping about 4 cm. in diameter, with a 

 corresponding plug stopcock suddenly opened between stops to arrest 

 the motion. 



