THE STRUOTUEE OF THE NUCLEUS. 49 



geneous state of nucleation through the agency of convection cui'rents, it may be 

 safely assumed that jYis not a function of r but of time only. If this were not so 

 the coi'onas would show color distortion (as they do in marked degree in benzine 

 vapor) as well as the time changes observed. In case of water vapor, the ever- 

 present convection will not allow either the distribution (1) or (2) to persist. 

 Hence, whatevei- removal of nuclei takes place at the inner wall of the large 

 receivers is a deduction or drain of nuclei from the lohole volume of vapor, uni- 

 formly. This experimental condition simplifies the computation and offers an easy 

 interpretation of the results obtained. In case of absorption with the adequate 

 convection, therefore (if R be the radius of the receiver),— (4^72^/3) dN/dt-= 

 Ah ^ttR'^ N, where h is the absorption velocity of the nucleus and A a co-efficient, 

 stating what part of k as found in my last volume for nuclei moving in air (k = 18 

 cm./min., about), is effective in view of the fact that the nuclei are now suspended 

 in water vapor. Hence, 



an equation identical in form with that actually found in the experiments. 



From equations (1) and (2), ^ — 'dAh (log e)/R ; and if ^ = 18 cm./min., R = 

 15 cm., then A = .0053. Thus the absorption velocity found from these experi- 

 ments is but 5/1000 of the value found when the saturated emanation is forcibly 

 passed through fine bore tubes less than .5 cm. in diameter, or that found from 

 electrical experiments for nuclei in air. This observed velocity of the nucleus in 

 water vapor would therefore be but .095 cm./mi4i., a result which will be further 

 discussed below (Chap. VI, § 19). 



28. Estimated size of cloud particles. — The rate of subsidence of the fog is 

 not a good criterion' of diameter, because this datum is complicated by the evapora- 

 tion of water particles (apparent subsidence at the top), and by their inevitable 

 growth, remembering that the coronas are all fleeting phenomena. Some notion of 

 their size, and this an upper limit, may be obtained: If the fog subsides at the rate 

 of 1 cm./sec, the radius of the particle will be r = .0009 cm. For any other velocity 

 expressed in terms of this normal rate, ?• = 9 X 10"* X Vv. Now the rates are 

 never a small fraction of cm./sec, so that the radii are not liable to be much below 

 say 10" 4 cm., a datum which at first sight is surprisingly large, but is corroborated by 

 the following independent estimates. Of. Chap. Ill, §11. 



It has been shown above that in the case of sphei-es the moisture pi-ecipitated 

 per cub. cm. of air partially exhausted, as stated, is 79 X 10-8g,-ams, and that with 

 5 X 10* nuclei per cub. cm. in the saturated emanation, this is equivalent to an 

 initial diameter of the water particles of about 2.5/10 ■* cm. This datum is an order 

 of values like the preceding, whereby two results are to this degree confirmed, viz : 

 the order of size of particles producing axial color and the number of particles 

 estimated for the saturated emanation. 



The same method applied to the results obtained from the double drum showed 



' Air, cleared of fog by the warmer walls of the receiver after exhaustion, also rises to the top. 



