CHAPTER II. 



NUMBERS AND GRADATIONS OF SIZE OF NUCLEI IN 



DUST-FREE AIR. 



EXPERIMENTS WITH DUST-FREE AIR NOT ADDITIONALLY ENERGIZED. 



Alternations of large and small coronas observed in case of identical 

 condensations produced in dust-free air saturated with moisture. 



16. Apparatus. By dust-free air I mean air which has been passed 

 through a packed-cotton filter. My filters are 16 inches long, conical, 

 tapering from about 2 inches in diameter at the large end to about 

 Y?, inch at the other. They contain absorbent cotton rammed in from 

 both ends and kept in place by wire. When filtered air is required, 

 the stopcock is only just opened so that influx of dust-free air may 

 be extremely slow.* This insures proper filtration and does not 

 interfere with the saturation of the air in the fog chamber. In this 

 section condensation was produced in a long glass cylinder, 16 inches 

 from end to end and 5^2 inches in diameter, placed horizontally and 

 normal to the line of sight. It contained a rectangular framework 

 of copper wire covered with wet cotton cloth, except on the two 

 opposed broadsides through which the coronas were observed. The 

 distance between the bottom (water) and the roof of the rectangular 

 framework was about 9 cm. The provisions for keeping the air 

 saturated are thus ample. 



The vacuum chamber was a large boiler of galvanized iron, 

 having a capacity, V, of over 100,000 cc., while the capacity, v, of 

 the condensation chamber is about 6,700 cc., so that the volume 

 ratio, v\V, is but 0.063. The two chambers are connected by 

 about a foot of rubber tubing over i inch in bore, usually containing 

 a i -inch plug gascock. An instantaneous clapper valve of the same 

 dimensions and opened with a hammer was often used for comparison. 



Later the glass fog chamber was advantageously replaced by one of 

 waxed wood (see fig. i, Chapter I), with the opposed sides, through 

 which the coronas were observed, made of plate glass. The internal 

 dimensions in this case were 55X12X20 cc., and the volume ratio, 

 v\V> in connection with the vacuum chamber, about 0.13. There 

 is difficulty, however, in using a chamber of this kind for the present 

 purposes, where even very small leakage is a serious discrepancy. 



*When the rate of filtration is gradually decreased until it all but vanishes, results 

 of special interest are observed which will be detailed elsewhere. 



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