CHAPTER II. 



LATER AND FINAL STAGES IN THE EFFICIENCY OF THE FOG CHAMBER 

 DUE TO A GRADUAL INCREASE IN THE BORE OF THE EXHAUST PIPES. 



CONNECTING PIPES NOT LARGER THAN 1.5 INCHES IN DIAMETER. 



35. Introductory. It will be the object of the present chapter to 

 further determine to what an extent a perfectly efficient apparatus 

 (i. e., one in which the cooling and the moisture precipitated per cubic 

 centimeter actually accords with the drop in pressure) may be ap- 

 proached by gradually enlarging the bore of the escape pipes between the 

 vacuum chamber and the fog chamber. One method of doing this will 

 consist in finding whether the distribution curves eventually reach a 

 fixed limit and a limit maintained for larger as well as smaller nuclei; 

 another by comparing the final results with corresponding data deduced 

 for Wilson 's piston apparatus. 



In treating the large numbers of observations which follow, it will be 

 convenient to refer the nucleations (as above) to the drop of pressure 

 observed under apparently isothermal conditions at the fog chamber. 

 This method of comparison is sufficient if the same fog and vacuum 

 chambers are used throughout, as has actually been done in the sequel. 

 The exhaust cock is always to be closed immediately after exhaustion. 

 In the present experiments the volume ratio of the two vessels was about 

 v/V = 0.064, where v is the volume of the fog chamber and V that of the 

 vacuum chamber. 



.... It was customary, as just stated, to open the stopcock between the 

 fog chamber and the vacuum chamber as rapidly as possible and then 

 to close it at once ; dp therefore denotes the drop of pressure read off on 

 the mercury gage at the fog chamber after sufficient waiting. As above, 

 5 is the angular diameter of the coronas on a goniometer radius of 30 

 cm., when the eye and the source of light are respectively 40 cm. and 

 250 cm. on opposite sides of the fog chamber. On the basis of these 

 data n is computed from the quantity* of water precipitated per cubic 

 centimeter and the value s, in the way shown elsewhere, f It is always 

 assumed that the nuclei are more rapidly reproduced than removed by 

 the exhaustion, or (without hypothesis) from another point of view, 



Wilson: Phil. Trans. Roy. Soc. London, vol. 189, 1897, p. 298. 

 f Smithsonian Contributions, vol. xxxiv, No. 1651, 1905, chap. viii. 

 34 



