162 THE STRUOTURK OK THE NUCLEUS. 



piiictical conclusions; for if through any radiation agency two tliU'erent emanations 

 are geaei-ated (with opposite charges or not), they would in a saturated medium 

 correspond to two different nuclei, and the number of each kind and their diffusion 

 rates in ireneral would also be different. If they should at the same time be 

 opposed in ionization, a separation of charges will result. Indeed if two or more 

 ''roups of ionized nuclei be geiieiated in any manner whatevei', they are liable to 

 have different number and speed constants and lead to a separation of charges, 

 be it only by diffusion. But the case is more definite, as the following paragraphs 

 may indicate. 



Inasmuch as the nucleus from my point of view occurs under conditions of 

 potential growth from a few molecules of dry solute to a weak solution {Gf. Chap- 

 ter V, §§ 47, 48), as the air becomes more and more saturated, this growth and 

 diminution must be a common occurrence in nature. The persistent atmospheric 

 nuclei will be more dilute from the surface of the earth upward. The (piestion 

 then occurs whether such gi-owth or change of concentration is accompanied by 

 electric charge, quite apait from what is generally known as ionization (demon- 

 strable presence of non-saturated chemical valencies) ; in other words whether any 

 change of size of these excessively fine particles is reciprocally accoinj)anied by sur- 

 face electrification. 



In his highly finished investigation published in 1892, Lenard (I.e.) showed 

 that in the pi'esence of air, pure water is electropositive, a circumstance which he 

 intei'iirets as a mere Volta contact effect. It needs but a trace of saline solute to 

 reverse the potential. Solutions in the i)reseuce of air are electronegative, and 

 more so as a rule as the concentration increases up to a definite value (6.5 % in case 

 of NaCl), for which the negative charge is a maximum. After this, as the concen- 

 tration increases the potential gradually tends towai'd zero (attained for a solution 

 stronger than 25 % in case of NaCl). Removal of nuclei by condensation and sub- 

 sidence is thus virtually a removal of negative electricity, provided the positive air 

 charge is not simultaneously removed. Here then the possibility of a mechanism, 

 in virtue of which growth or increasing dilution is associated with increasing nega- 

 tive charge for the nucleus, is actually at hand ; l)ut the difficulty at present rests 

 with the removal of the air charge. 



Briefly, the point I wish to make is that the occurrence of charge is incidental 

 and not causal to the existence of the nucleus. What conditions its persistence 

 and condensational activity is purely thermodynamic ; what conditions the efficiency 

 of electric transfei- is a secondary pi-o{)erty, open to investigation though as yet but 

 little understood, and which even in the same nucleus (solution) is present in very 

 vanable amount, or may be quite absent. The phenomenon in its electric aspects 

 depends therefore on the critical density at which evaporation ceases (Chaj^ter V, 

 §48). 



In the above paragrai)hs I have endeavored to indicate how the current lines 

 of argument bearing more or less remotely on atmospheric electricity at present 

 stand ; to point out that none of them have as yet been traced to a definite issue, 

 and to show the direction in which I hope myself to contribute. 



