38 A CONTINUOUS RECORD OF ATMOSPHERIC' NUCLEATION. 



either sign. If the nuclei were without charges, however, the medium would 

 not conduct. In a condenser, positive or negative charges are sooner dissi- 

 pated according as there is excess of negative or positive nuclei in the meditmi, 

 respectively. 



20. Comparison of phosphorus and water nuclei. — Between phosphorus and 

 water nuclei there is in the first place the essential difference that whereas the 

 current in the first case obeys Ohm's law, rotighh', it does not do so' in the 

 second, being more and more independent of the electromotive force as E 

 increases above about 1 5 volts per cm. Similarly, the coronas for water nuclei 

 usually terminate with the middle g-b-p type, whereas in case of phosphorus 

 they go to indefinitely higher orders, beyond the first in the series. Parallel 

 to this there may run a difference in the size of nuclei. The inference is war- 

 ranted that phosphorus nuclei are small as compared with water nuclei, 

 iiiasmuch as the latter owe their origin to mechanical conditions, while the phos- 

 phorus nuclei arise under molecular conditions and molecular dimensions. As 

 the observed electric currents are about of the same order in both cases, it follows 

 that the charges per nucleus are verj' much larger for water nuclei than for 

 phosphorus. If water ni:clei covdd be examined immediately after production, 

 i. e., in the same degree of freshness as is customary for the phosphorus nuclei, 

 the contrast wotdd be enormous. 



In both cases, however, whenever ionization and nucleation are associated 

 phenomena, the ntimber of ions generated varies directly with the concomitant 

 number of nuclei. 



In other respects there is great similarity in the behavior of the two types 

 of nuclei. The enormous charges of ionizations at the beginning vanish to a 

 residuum of a few per cent, in a few minutes if confined by a receptacle, while 

 the nuclei are not affected either as to number or condensational properties by 

 the presence or absence of the primitive charge. It is not unreasonable to 

 suspect, therefore, that the water nucleus, like the phosphorus nucleus, may be 

 the permanent residue produced b)' the expulsion of the electrons representing 

 the ionization: for whenever nucleation and ionization arise in a common 

 source, any increment of the former is accompanied bj^ a corresponding incre- 

 ment of the latter. 



