160 VAPOR NUCLEI AND IONS. 



dp from 26 to 28 cm. and observing the changes of 5 (angular coronal 

 diameter) when p is constant, a table was investigated from which 

 reductions could at once be made to dp = 2j cm. and = 76 cm.; for 

 instance, 



The value of 5 corrected for both pressures is given in this table. 



In the same way the case of apparatus II (to be described presently) 

 was treated, the reductions being much larger here. Thus the data 

 (barometer, 75.5; temperature, 21.4 C.) 



^=24.9 ^ = 1.7 dp =25.6 *=3- 1 



5-2 



2.9 



were consecutively observed, showing that the coronas after long waiting 

 are much larger than when obtained in succession. The efficient nuclea- 

 tion of the fog chamber increases in the lapse of time, probably from the 

 evanescence of water nuclei associated even with small coronas. From 

 these results corrections of the form 



dp- 



were made out. These examples show how critically important these 

 corrections are, and how difficult it will be to decide whether anything 

 more than the barometer fluctuation is being observed. 



102. Further data. It follows from section 101 that there would be a 

 chance for error in the unavoidable leakage of the stopcock, and the 

 best method of coming to a decision would consist in the installation of a 

 second fog chamber, side by side with the other, but containing a smaller 

 exhaust pipe (2 inches in diameter, 18 inches long) and therefore a more 

 perfect stopcock. 



Fig. 65 shows two fog chambers (F and F') and appurtenances in place, 

 each with an independent vacuum chamber (Vand V') and goniometer. 

 Other parts will be easily recognized. 



Table 55 and chart 66 contain the new data, the old fog chamber 

 (4-inch cock) being marked I, the new fog chamber (2-inch cock), marked 

 II. The latter was first tested at different values of dp, and dp = 25.6 



