Chemistry and Physics. 



471 



Since the apparatus employed was simply a specially adapted 

 form of the well-known Wilson expansion chamber, it does not 

 seem desirable to enter into details of the experimental method 

 in this place. All of the results obtained by Wilson's experi- 

 ments are in complete accord with the previously accepted inter- 

 pretations of the various ionization experiments, which could not, 

 in the veiy nature of the case, appeal directly to the sense of 

 vision. Such an appeal is, of course, not at all necessary for 

 scientific progress, but a concrete or graphical representation of a 

 phenomenon is very satisfying to many minds. 



The clouds formed with large expansions, ("Vj/V,^ 1'38), in 

 the absence of ions showed a uniform distribution of droits. 



In photographing the ionization produced by a-rays a radium- 

 tipped metal tongue from a spinthariscope was placed inside the 

 cloud-chamber and the expansion was made after removal of the 

 dust particles. The clouds are beautiful and chiefly consist in 

 segments of straight lines which radiate from the radium "point." 

 It is probable that the most sharply defined lines, about o - l mm 

 wide, alone represent the actual distribution of ions immediately 

 after the passage of the a-particles, before any appreciable diffu- 

 sion has had time to take place. 



When ionization was produced by /3-rays two or three abso- 

 lutely straight, thread-like lines of cloud were generally seen 

 radiating from the source. In addition, other similar lines were 

 occasionally seen crossing the vessel in other directions, and these 

 were probably due to secondary /3-rays from the walls of the 

 vessel. 



When the air in the cloud-chamber is allowed to expand while 

 exposed to the radiation from an X-ray bulb, the whole of the 

 region traversed by the primary beam is seen to be filled with 

 minute streaks and patches of cloud, a few due to secondary 

 X-rays appearing also outside the primary beam. The photo- 

 graph, which is reproduced in the paper, shows that the cloud- 

 lets are mainly small, thread-like objects, each not more than a 

 few millimeters long, and many of them are much less than 

 0-i mm broa^ Few cloudlets are straight and some form com- 

 plete loops. The results are in agreement with Bragg's hypothe- 

 sis that the whole of the ionization by X-rays may be regarded 

 as due to {$- or cathode-rays arising from the X-rays. The ques- 

 tion whether the original X-radiation has a continuous wave- 

 front, or is constituted in the different ways suggested by Sir 

 J. J. Thomson and Bragg, remains as yet undecided. — Proc. Poy. 

 Soc, vol. lxxxv, 285. H. S. TJ. 



10. On the Dynamical Nature of the Molecular Systems 

 which emit Spectra of the Paneled Type. — Many attempts have 

 been made to construct a model of a molecule which will possess 

 such dynamical properties as to radiate channeled spectra. Most, 

 if not all, of these analytical investigations have been unsatisfac- 

 tory either because they have led to very complicated transcen- 

 dental equations which are too general to admit of comparison 



