140 THK STBUCTUKE OI-' THE NUOLE0S. 



4. Structure of nuclei. — The next inference to be diawu is some notion of the 

 chemical composition of these nuclei. For convenience merely, they are usually 

 supplied hy introducing into the receivei- air which has passed over phosphorus, or 

 burning sulphur, or trlowing charct>al, etc. Tiiey may be obtained, however, with- 

 out putting anything material into the receiver, by passing the X-rays or other 

 form of radiation through it. An incidental ex[)eriment of this kind among many 

 may be cited here, A thin-walled glass flask, 23 cm. in diameter, containing a 

 small charge of alcohol, was exposed io the X-rays of a focus-tube of mild ladiating 

 intensity. Examined by exhaustion (pressure decrement IG cm.) after 5, 10, and 

 15 minutes had successively elapsed, no coionas were obtainable. After 30 minutes 

 of exposure, however, a coiona was obtained, and several subsequent exhaustions 

 were needed thereafter to remove the nuclei. The production of nuclei in case of 

 weak radiation is thus very gradual. It takes time to make them ; but when once 

 produced, they show a degree of persistence identical with that of nuclei of any 

 other origin. 



Hence, so far as the behavior of the resulting nucleus is concei'ned, there is no 

 (pialitative difference referalde to its origin. One must therefore look upon the 

 iraseous contents of the receiver as containing the stuff out of which the nuclei are 

 made. The inquiry is thus nairowed down to this : which of the gases involved 

 (air or vapor) is made colloidal in the manner specified. If the air is selected, then 

 there is no immediate reason for the apparent difference of size of nuclei of the 

 same origin in electrolytic and non-electrolytic solvents respective!)'. If the vapor 

 is selected, then the difference in size corresponds to the electi'ochemical difference 

 of the liquids. 



5. Possible electronic agencies. — If one adheres to the electrical point of view, 

 the agency which holds the nucleus or molecular cluster together is presumably 

 associated with the electron. One should therefore anticipate greater conductivity 

 in case of the much more mobile nuclei of the first type (vapor of ionizing licpiids) 

 than in the sluggishly moving nuclei of the second type (vapor of nonionizing 

 li(juids), though it is not certain that the electron resides permanently with the 

 same nucleus. I am not aware that experiments of this kind have been tried. 

 One may note that the smallest nuclei occur in liquids of greatest, the largest in 

 liquids of least, specific inductive capacity ; but all this is tentative.' 



Finally, the order of condensation here implied should be noticed. The elec- 

 tron, by its mere pi'esence, condenses the nucleus or molecular cluster (\vhether 

 li(]uefied or not), the latter being always so small an aggregation of molecules as to 

 remain optically inappreciable. The nucleus for Kelvin's thermodynamic reasons 

 condenses the visible water globules seen as coronas on exhaustion. The diameters 

 of these two groups must be in the ratio of less than 1/1000. The uniformity of 

 nuclei produced by shaking may also be thus accounted foi-, inasmuch as some 

 sort of chaige must accompany the shaking. Their persistence in the presence of 

 electrolytes like HCl or the salts may be plausibly anticipated. 



These are some of the advantages of an electronic hypothesis. Nuclei are so 



' It breaks down for acetone. 



