394 



Barus and Watson — Air Stored over Water. 



the enclosed pure water centrifugally, or but a part of it, at 

 pleasure. The difference of the rotational resistances for the 

 two cases is noteworthy. 



The angular diameter, 0, of the coronas was determined 

 with a goniometer having a radius R = 30 cm long, so that if s 

 is the chord corresponding to i£, tan 0/2 = s/2R. Goniometer 

 and source of light were 85 and 250 cm , respectively, from the 

 cylinder, and the exhaustions all corresponded to the pressure 

 difference of about 8p = 17 cm , at about 20°. 



The results are definite. The first and last parts of Table II 

 show that the time loss of nuclei when the cylinder is rotating 

 so rapidly that the water is held up as a smooth sheet against 

 its sides, is not much larger than when the cylinder is station- 

 ary, in spite of the fact that in the first case some nuclei must 

 be lost in the turbulent motion on starting and stopping. The 

 law of decrease is as usual apparently geometric. 



When the critical speed at which water is caught up on the 

 sides is not attained, in other words, when only a part of the 

 water contained is carried around by rotation, then the cleans- 

 ing effect is very marked as the middle parts of the table show. 

 Furthermore, nuclei are lost more rapidly per minute as the 

 speed of rotation producing turbulent motion is greater. 



Thus it follows that the nuclei are lost by the continued 

 bubbling of the air enclosed within the cylinder through the 

 water contained. This rotational method of making the air 

 dust-free* is frequently very convenient, particularly in those 

 cases where slow rotation of the condensation chamber is neces- 

 sary to keep the air within saturated, and in other cases to 

 be treated elsewhere. 



In conclusion, we may observe that if the continuous passage 

 of air in bubbles through water produces ions (as has been 

 shown by J. J. Thomson, Himstedt and others), these ions are 

 not in evidence in the role of condensation nuclei; for the 

 effect of churning pure water, far from being a means of gen- 

 erating nuclei, has in the above experiments been shown to be 

 a very effective method of making the air dust-free. From 

 this point of view we regard the experiments as noteworthy. 



Brown University, Providence, R. I. 





