762 



SCIENCE. 



[N. S. Vol. XXII. No. 571. 



dent ' ; for an audience on the back benches, 

 leaving the front benches empty, can not be 

 regarded as encouraging to the speaker. A 

 young page at the service of the president and 

 secretary is an appropriate luxury; he can be 

 waked when messages have to be sent. A 

 lobby into which members can retire for con- 

 versation is indispensable for a comfortable 

 meeting; it should not be so near the meeting 

 room that laughing in one drowns speaking 

 in the other. As to the manner of presenta- 

 tion of scientific communications by the 

 speakers, that is too sacred a question for us 

 to enter upon. Individuality must be pre- 

 served at all hazards. But if a distinction 

 could be drawn between the form in which a 

 problem is prepared for publication and the 

 form in which it is presented orally to a 

 listening audience, and if the effect to be pro- 

 duced upon the audience could be duly con- 

 sidered by the speaker, scientific meetings 

 would be even more successful than they are 

 now. 



One other practical suggestion may be al- 

 lowed. It would be an assistance if the local 

 committees would write down the more im- 

 portant results of their experience in a trans- 

 mittendum, to be passed on to their successors. 

 Thus, even if new mistakes were occasionally 

 invented, old mistakes might be more gen- 

 erally avoided, and a greater enjoyment and 

 profit might be secured for all concerned by 

 the gradual removal of various trifling incon- 

 veniences and distractions which have no 

 place in well-conducted meetings. 



A Fellow op the Association. 



SPECIAL ARTICLES. 

 NOTE ON THE FALLING-TO-PIECES OF THE IONS. 



1. The data summarized in the following 

 graphs were obtained by acting in the manner 

 stated, on the dust-free moist air contained 

 within a glass fog chamber, with a sample of 

 weak radium (10,000 X> 10 mg.), sealed in an 

 aluminum tube. This was placed on the out- 

 side of the chamber in contact with its walls 

 (.2 to .3 cm. thick), and was then removed 

 suddenly at given intervals before exhaustion. 

 Only very penetrating primary rays (^ and 



y) are, therefore, in question. The curves 

 show the number of efficient nuclei in thou- 

 sands per cubic centimeter, observed after 

 the lapses of time shown by the abscissas, and 

 it is supposed that the nuclei are reproduced 

 faster than they can be removed by the ex- 

 haustion. In the upper curve the pressure 

 differences applied {hp ^31) are much above 

 the fog limit of dust-free air, which is below 

 8Po = 24 for the given apparatus. In the 

 lower curve the pressure differences are nearly 

 at the fog _ limit of dust -free air, while the 

 other curve (8p = 28) applies for interme- 

 diate conditions. The effect of the radiation 

 is, therefore, virtually at least, a coagulation 

 (to use a figurative expression) of the col- 

 loidal nuclei of dust-free air, into the aggre- 

 gates much larger in size representing the 

 ions. Hence in the presence of radium under 

 the given conditions, the number of efficient 

 nuclei decreases either because the ions from 

 their size capture all the available moisture 

 more and more fully, or because the colloidal 

 nuclei have actually been aggregated into 

 fewer but larger systems, which will in turn 

 fall apart in the absence of radium. Professor 

 Barus^ has recently pointed out that inasmuch 

 as the radiation within the fog chamber is 

 largely secondary, and must, therefore, at a 

 given point come from all directions, a cor- 

 puscular pressure must exist within, having 

 a tendency to produce agglomeration; and the 

 same results should occur for an easily scat- 

 tered undulatory radiation. This would ex- 

 plain why the X-rays and ultra-violet light 

 produce fleeting and persistent nuclei alike in 

 kind, except that only the former are ionized. 



2. It follows from what has been stated that 

 above the fog limit of dust-free air, the num- 

 ber of efficient nuclei must increase with the 

 removal of radium at a rate which corresponds 

 to the falling to pieces of the ions. The 

 peculiar feature of the results here in question 

 is the manner in which the efficient nucleation 

 decays from the coarser ionized to the finer 

 non-ionized colloidal stages, when the pressure 

 difference is decidedly above the fog limit of 

 air, so that the latter may be recognized. The 

 curves invariably pass through a minimum 



"■Am. Jour. ScL, (4), XX., p. 298, 1905. 



