C. Barus— Successive Cycles of Coronas. 309 



Akt. XXXI. — On the Successive Cycles of Coronas • by 



C. Barus. 



1. Introductory. — Using the method of successive identical 

 exhaustions or withdrawal of nuclei, by which the nucleations 

 left in the fog chamber should decrease in geometrical progres- 

 sion* from the high initial value given to dust-free air by the 

 emanations of phosphorus, I have recently attempted to gain 

 an estimate of the trustworthiness of the results, by using drops 

 of pressure (Sp from atmospheric p) of widely different values. 

 These range from one extreme hp — 10 om to the other 8p = 20 cm . 

 Leaving the data, for which there is no room here, for publica- 

 tion elsewhere, f it appears that if the diameter of particle d 

 of a given type and order of corona, worked out from the vari- 

 ables and constants of the experiment, agree reasonably well, 

 the general method of reduction is assured. 



The whole of the work was done in time series. Thus the 

 exhaustion cock between the vacuum and fog chambers was 

 kept open five seconds after exhaustion, only, and the time 

 between two successive exhaustions was one minute. Other 

 intervals were also tested without modifying the results. The 

 time during which the cock remained open is of special impor- 

 tance, for the exchange of air between the two chambers 

 depends ujdou it, and hence also the rate at which nuclei are 

 removed per exhaustion. These details were determined in 

 preliminary experiments. The isothermal pressure in the fog 

 chamber after five seconds of communication between the 

 chambers, obviously differs in marked degree from the isother- 

 mal pressure if the chambers are permanently left open in 

 communication. 



Additional correction was made for subsidence of fog par- 

 ticles during the short time, in all about fifteen seconds, needed 

 for the observation of the coronas. They were then at once 

 dispelled by opening the filter cock, evaporating the fog par- 

 ticles and restoring the nuclei left behind to their original size. 

 Other losses, as for instance the evaporation loss which occurs 

 when fog particles are precipitated on ions or on the vapor 

 nuclei of dust-free air, or the time loss (decay), were found to 

 be negligible. The amount of water precipitated, however, 

 varies both with the adiabatic drop of pressure and with initial 

 temperature, all of which was carefully allowed for. The 

 ratio of sections of the fog chamber and the exhaust pipe was 

 about 6/1, sufficient to reach the highest coronas. In fact the 

 large red type of the first series was certainly obtained. 



*This Journal, xiii, pp. 81-94, 1902. 



f To be given in a forthcoming Carnegie publication. 



