EFFICIENCY OF PLUG-COCK FOG CHAMBER. 13 



10. Conclusion. If the fog chamber is combined with a large 

 vacuum chamber, through a sufficiently wide passageway containing an 

 ordinary plug gas-cock to be opened and closed rapidly by the hand, all 

 the measurable coronas of cloudy condensation, due to the presence of 

 colloidal or vapor nuclei in wet, strictly dust-free air, may be evoked. 

 While such an apparatus admits of capacious fog chambers and ex- 

 tremely simple manipulation, it has not been shown to be inferior in 

 efficiency to any other apparatus whatever. 



The conditions of exhaustion must, however, be computed from the 

 initial pressures of the fog and vacuum chambers when separated and 

 their final pressure (after exhaustion) when in communication, in all 

 cases at the same temperature and the volume ratio of the chambers. 

 The chief pressures and temperatures are shown in fig. 2 for different 

 initial pressures of the vacuum chamber, the fog chamber being at 

 atmospheric pressure. 



