A CONTINUOUS RECORD OF ATMOSPHERIC NUCLEATION. 3 



of the coronal phenomena, in relation to the number of nuclei concerned. The 

 usual and strong response of the steam jet is for axial blues and greens as far as 

 the purples of the second order. These are already too weak to be of effective 

 service for measurement. But at this stage of smallness of fog particle, the 

 coronal display has but begun. The strong blues of the axial colors correspond 

 to the diffuse gray fogs of the condensation chamber out of which the coronas 

 are gradually evoked when the number of particles l has sufficiently diminished. 

 The two instruments are thus in a measure supplementary; the condensation 

 chamber gives intense evidence of the presence of nuclei long after the steam 

 jet would imply their absence. It is for this reason that ordinary smokes like 

 sal ammoniac do not affect the steam jet 2 where a number of nuclei exceeding 

 a certain lower limit is necessary. The latter again is particularly active for 

 those intense and fresh nucleations which produce the browns and yellows of 

 the first order, implying conditions which it is impossible to produce in the 

 condensation chamber at all, until the lower limit of spontaneous condensation 

 of dust -free moist air has been exceeded. 



5. Decay and absorption. To account for the rapid diminution of the 

 number of nuclei in the phosphorus emanation in the lapse of time, two hy- 

 potheses are prominent. With finely divided and in so far highly potentialized 

 matter (possibly ionized positively and negatively), combinations of nuclei may 

 occur to the detriment of the number of independent nuclei. Such a decrease 

 would take place as the square of the number. On the other hand, it is equally 

 probable that the initial and very small nuclei are in rapid motion much like 

 molecules, and that the loss takes place by absorption or arrest at the walls of 

 the vessel. In my memoir on the subject, I included both hypotheses in the 

 computation; but finding that the phenomena could be adequately explained 

 by the latter, I ignored all spontaneous decay. Though this policy would not 

 be generally admissible, it is unlikely that nuclei can vanish initially at the 

 same rapid rate as the ionization. Indeed, evidence will show that it does not. 

 In case of water nuclei, which are much the more sparsely distributed, the 

 original number of nuclei can be proved by coronas to have varied but little in 

 the short time in which the ionization falls off to a few per cent. Hence the 

 nuclei must be regarded as parting with their charges more rapidly than they 

 are themselves absorbed in the lapse of time, and one will have to distinguish 

 between the velocity of the uncharged and of the charged nucleus in the electric 

 field, the latter being incremented by the electric forces. The cases will be 

 worked out in the chapters below. 



6. Apparatus. The apparatus used in the present experiments was capa- 

 ble of a great number of variations. The essential purpose is to enable the 

 observer either to introduce phosphorus emanation at once into the electrical 

 condenser or else to introduce it after it has been saturated with water, suddenly 



1 Phil. Mag. (6), iv, p. 24, 1902; cf. Structure of the Nucleus, Chapter III. 



2 Thus smoke due to sal ammoniac if introduced into the steam tube will actually clear 

 the blue field produced by phosphorus nuclei, i. e., will wipe out the condensation. 



