462 Mr Lusby, Some Experiments on 



M. de Broglie has further given a general method for detecting 

 and controlling these nuclei. If by the action of drying, some of 

 these large ions were broken up into a small charged portion and 

 a large neutral system, the small portion would be caught by the 

 testing condenser and give an effect of the nature observed. This 

 type of analysis of the large ion, viz. into one charged and one 

 neutral portion, is the only one admissible if we assume that the 

 ion possesses only one electronic unit of charge and further assume 

 that this unit is indivisible ; the latter supposition seems to 

 be supported by experiment, but the former is as yet purely 

 gratuitous. 



To test this theory, the air before entering the apparatus was 

 deprived of all its ions — large and small — by passing through 

 a long condenser charged to an appropriate potential. Small ions 

 are quickly produced spontaneously, but it takes a fairly long time 

 for these to combine with the neutral centres to form large ions. 

 In some previous experiments carried out by the writer*, it was 

 found that air thus deprived of large ions did not again acquire 

 the normal number till after about 20 minutes ; de Broglie 

 {loc. cit.) has investigated a similar effect, and states that it 

 requires a considerable time for the large ions to attain their 

 maximum number, but gives no exact figures. As the time 

 required for the air to pass from the electrical filter to the U-tube 

 is at the most only 5 seconds, one seems justified in concluding 

 that no appreciable reproduction of large ions occurs in this interval. 

 On trying the above experiment, it was found that the result was 

 quite independent of the large ions present in the air. 



There now remained only the question of recombination, which 

 however did not promise to give a solution of the problem ; for 

 recent work by Erikson-j- has shown that the coefficient of recom- 

 bination increases as the temperature decreases, which obviously 

 would give an effect entirely opposed to that observed. It is true 

 that the coefficient thus found was under conditions of constant 

 density, whereas in the present investigation conditions of constant 

 pressure obtained. Still one could roughly suit the constant 

 density coefficient thus found to the present case (where the 

 pressure at any temperature would be higher) by superposing on 

 it conditions of increased pressure. Now, according to M^Clung|, 

 the coefficient of recombination is independent of pressure between 

 the limits of 0"1 and 3 atmospheres ; whilst Langevin § showed 

 that below these limits the coefficient decreases rapidly as the 

 pressure is lowered. Thus an increase of pressure would in the 



* Lusby, Journ. Roy. Soc. N. S. W. June 1909. 

 t Erikson, Phil. Mag. Aug. 1909. 

 + M«Clung, Phil. Mag. March 1902. 

 § Langevin, C. R. cxxxiv. 1902, p. 646. 



