340 C. Barns — Apertures of Coronas. 



log n' = 2(1+ bt) log y* 



if the same corona, 2, and time interval, t, is implied. 



Hence S(log n) = 5 (log 2/) while ?i = (6m / 7ra s )s' = 120s 3 . 

 Therefore log y'/log y = (log .4+3 log $')/(log A + 3 logs). 



The computed values s = a *J nir/6m are given in the chart, 

 curves 1, 2, 3. From the latter for s = 5'0, s' = 8*0 to 9-0 cm . 

 Hence 



s' = 8, y'=-807, 



s' = 9, y' = -804, 



whereas y = *819 was the value computed in my work on 

 coronas* for the exhaustion 76-5 8 cm . 



Since roughly y = (p/p ) 1/7 , where p — 76 and 7 = 1*4, the 

 following values of Sp obtain : 



s = 5-0 cm , 



Sp = 18-0 cra , 



s'= 8-0 



19-1 



s'= 90 



19-4 



Thus if the pressure decrement on exhaustion had been 

 taken l cm higher than the observed value, the apertures com- 

 puted from successive exhaustions in the former memoir would 

 agree with the average apertures directly measured in the 

 present paper. Observationally this is out of the question, but 

 it is nevertheless difficult to know just what pressure is effec- 

 tive in the adiabatically cooled receiver (cf. Structure of the 

 Nucleus, p. 38, § 16), since neither the isothermal nor the adia- 

 batic conditions will rigorously suffice. The memoir shows 

 that isothermally y='764r; adiabatically y — '825 ; adiabat- 

 ically with allowance for condensed water y = -819, as already 

 specified. The present aperture data demand y = '805, which 

 is even nearer to the isothermal y than the value taken. 



Incidentally one may note the precision with which y must 

 be entered or the pressure difference determined, if the observa- 

 tions are to be sufficiently close to admit of a computation of d 

 and n. In other words, it is probable, that the ratio y may be 

 determined with greater accuracy from the successive aper- 

 tures as a whole, notwithstanding their periodic character, than 

 by direct measurement. This is what I meant by stating that 

 the two sets of observations would probably sustain each other, 

 for nobody would be justified in using the apertures of 

 abnormal coronas, unless such use was suggested and guided 

 by independent evidence. My own conviction is that n / = 2*2 n 

 may now be accepted with confidence. 



8. Summary. — The result of this paper is then favorable to 

 the use of the apertures of coronas in place of the colors of the 

 annuli, for estimating the number of particles corresponding to 



* Structure of the Nucleus, chapters 3 and 4, this Journal, xiii, p. 83, 86. 



