204 



SCIENCE. 



[N. S. Vol. XI. No. 267. 



that strong evidence is afforded in favor of 

 a specific velocity of the particles of a sup- 

 posedly non- ionized dust, so far as the 

 phosphorous emanation has been known. 

 Since they are always absorbed they must 

 clearly soon vanish out of any vessel, usu- 

 ally within five minutes if considered in 

 bulk. A large part of this dissipation is 

 referable to the grosser dust particles in 

 ordinary air.* Thus if phosphoric dust 

 and a suitable small quantity of smoke of 

 ammonium chloride (made in the usual 

 way) be passed into the color tube, the 

 field which is opaque with phosphoric dust 

 alone, becomes cleared when the sal-am- 

 monium smoke is added. The larger par- 

 ticles of the latter have therefore captured 

 the finer particles of the former (phos- 

 phorus emanation); and as sal-ammonium 

 smoke alone, if not itself opaque, is unable 

 to produce colored cloudy condensation or 

 opacity, the field clears at once. Now if 

 sal-ammonium smoke can capture phos- 

 phoric dust then it is conceivable that 

 agencies may exist which reverse the for- 

 tunes of war and liberate phosphoric dust. 

 Heat is such an agency. If nearly effete 

 dust be passed through a hot tube (say 

 above 400°), experiment showed me that 

 the condensation producing tendency is 

 again restored, precisely as if the dust were 

 dissociable. At a higher temperature still, 

 though not necessarily above red heat, the 

 tube itself becomes an energetic dust pro- 



* This secondary dissipation is neglected in the dif- 

 ferential equation (1), being of much smaller order 

 than the surface effect investigated. With the wide 

 tubes (diameter 2 inches), presently to be mentioned, 

 the differential equation replacing ( 1 ) above is 



— T^r^v dnjdx = kn27vr + k'li'jv 



■where k' is the number vanishing per second per unit 

 of concentration of dust in air. The last term de- 

 creases as V, the velocity of the air current increases. 

 This equation is easily reduced as a ease of Eiccati's 

 equation, and the integration may therefore be made 

 ■without difficulty. 



ducer at its inner walls, even when of glass, 

 so that experiments of the present kind are 

 delicate. Indeed long ago I asserted that 

 the strong dust producing activity of flames 

 was a conversion of coarsely disseminated 

 into finely disseminated atmospheric dust, 

 a conversion of the planets of this micro- 

 cosm into nebulae, as it were. 



One may readily conceive the X-rays to 

 be another such agency. After some trials 

 I devised a form of apparatus appropriate 

 for my purposes, by which the condensa- 

 tional tendency of air energized by X-rays,* 

 shows almost as powerfully in the color 

 tube as does the older dust laden air. So 

 far as the effect of these different kinds of 

 dust on the color field is concerned, one 

 would be unable to distinguish any note- 

 worthy difference of behavior. Both may 

 be carried through tin tubes 2 inches in 

 diameter and over 60 feet long, taking one 

 or more minutes in the transfer, without 

 encountering fatal diminution in the con- 

 densation producing power of either. Other 

 and now well known experiments of an en- 

 tirely different nature go to show that X-ray 

 dust is ionized, or transferred in a region 

 of ionized gas, whereas the ordinary dust, 

 with which I have chiefly worked, is not ; 

 but I ask, if both classes of dust are under 

 proper limitations, equally able to induce 

 condensation in supersaturated aqueous 

 vapor, how can one single out the excep- 

 tional quality of ionization as the cause of 

 this tendency? It has been brilliantly 

 proved by J. J. Thomson, Rutherford, 

 Chattock, and indirectly by C. F. E. Wil- 

 son,that ionized dust has a definite velocity ; 

 but in as far as the above experiments have 

 weight, so has the supposedly non-ionized 

 dust. 



* Of course, the X-ray tube must be boxed up 

 most carefully, the rays shining through an aluminum 

 window, and the terminals imbedded in paraffine. 

 Any highly potentialized conductor, like a hot body, 

 is apt to dust the air. 



