Februaey 9, 1900.] 



SCIENCE. 



203 



either of these variations. The table also 

 gives the ranges of the velocities of dust- 

 laden air through the absorption tubes re- 

 sulting from the differences of length, and 

 the limit of values computed for h showing 

 the errors of measurement. The final col- 

 umn contains the mean value of h obtained 

 from the data as a whole. 



to be seen whether greater refinements of 

 method* will rather bring the ^-values to 

 coincide for all condensing surfaces or ac- 

 centuate differences. 



At all events, it is already clear that the 

 velocity of the phosphoric dust particle is 

 independent of its density of distribution. 



In the Bulletin cited, the work of which 



Table. — Absorption of phosphoric ddst* in tubbs. 



In view of the widely different values of 

 the velocity with which the dust laden air 

 traversed the absorption tubes, the high 

 velocities employed .and the marked differ- 

 ence of material which makes up the ab- 

 sorbing walls, the close proximity of the 

 values of h is particularly noteworthy when 

 the meaning of this constant is called to 

 mind : h being the absorption per square 

 centim. per second per unit density of dis- 

 tribution, is simply proportional to the 

 velocity of diffusion of the phosphorus 

 emanation, or in other words, to the veloc- 

 ity with which the particles ejected from 

 phosphorus by an oxygen reaction travel 

 normally through the surrounding air. In 

 the cases of glass, of impure vulcanized 

 gray rubber, of pure brown rubber, this 

 velocity is so far as observation warrants, 

 the same. In the case of lead tubes the 

 velocity set forth by h is slightly larger, a 

 circumstance which may have an electrical 

 or a chemical bearing, or be referable to the 

 greater density of these tubes. It is entirely 

 premature to speculate upon it. It remains 



* Similar results were obtained with dust particles 

 ejected by concentrated sulphuric acid. 

 t Litres per minute. 

 X Centims. per second. 



was done in 1893, and elsewhere, f I denied 

 that colored cloudy condensation was ever 

 due to ions, a theory then rife and particu- 

 larly discussed by the younger v. Helm- 

 holtz, Bidwell and others. None of these 

 investigators have, to my thinking, made 

 out a clear case. Since the advent of the 

 X-rays and of the brilliant work done at 

 the Cavendish Laboratory, however, the 

 status of the question has changed ma- 

 terially. Nevertheless I am still loth to 

 abandon my former conviction that con- 

 densation is always primarily due to nuclei ; 

 and that whether they are ionized or not 

 (none were certainly known until recently), 

 is a matter of secondary and perhaps negli- 

 gible consequence. Thus for instance, con- 

 centrated sulphuric acid is a dust producer 

 comparable to phosphorus ; and yet this is 

 the very reagent that has always been used 

 in drying the chambers of apparatus when 

 high insulation is specially wanted. Cer- 

 tainly one would be rash to thrust the wily 

 ion in such a chamber. Indeed the interest 

 which- attaches to the above results is this, 



*The color estimates in the table -were made by 

 the eye. It will not be difficult to repeat them rela- 

 tive to some fixed standard blue. 



■\NaUt.re, XLIX., p. 363, 1894. 



