2 Art. 10.— S. Kinoshita and H. Ikenti : 



was examined first l)y Keinganum^^ On a photograph ol)tained 

 in this way, silver grains were found arranged on distinct hnes, 

 showing themselves as the a ray tracks. He also found that 

 some of the tracks showed the efïect of scattering. Experiments 

 on this subject were later made in detail by Michl"' and by 

 Mayer^\ Some microphotographs of the a ray tracks showing 

 deflexions were ol)tained by Walmsley and Makower*\ 



For the last three years, we have been engaged in devising 

 some simple methods of obtaining radial a ray tracks and making 

 some investigations upon them. The present paper contains 

 the main results in this line of investigation, most of which 

 appeared separately in other publications*^ 



2. Methods of obtaining radial a ray tracks. In investigating 

 the photographic traces of « rays it was thought most ad- 

 vantageous to work with the smallest possible source of the rays. 

 For, if a point source be established and placed on a photographic 

 plate, the expelled « particles will leave on it a set of radial traces, 

 which can Ije followed with greater ease and certainty^\ 



The source which we first utilized was a fine needle point 

 coated with a trace of active deposit of radium'''. This was 

 prepared by lightly rubbing the point on a small ball of iron 

 which had previously been exposed to a few millicuries of radium 

 emanation. By 1 »ringing the needle in contact with a photo- 

 graphic plate, a part of the active deposit was detached from the 

 needle and left on the plate at the point of contact. Leaving the 

 plate for a certain time to allow a sufficient number of a particles 



1) M. ßeing-anum, Phys. Zeits. 12 (1911), p. 1076 ; Verb. d. D. Phys. Ges. 13 (1911), p. 848. 



2) W. Michl, Akad. Wiss. Wien. Ber. 121, 2a, (1912), p. 1431. 



3) F. Mayer, Ann. d. Phys. 41 (1913), p. 931. 



4) H. P. Walmsley and W. Makower, Proc. Phys. Soc. 26 (1914), p. 261. 



5) S. Kinoshita and H. Ikeuti, Proc. Tokyo Math.-Phys. Soc. 7 (1914 , p. 360; also Phil. 

 Mag. 29 (1915), p. 420; H. Ikeuti, Phil. Mag. 32 (1916), p. 129; Proc. Tokyo Math.-Phys. 

 Soc. 8 (1916), p. 465. 



6j In the first publication, we have referred to the paper of Michl of which we learnt 

 through the Beiblätter z. d. Ann. d. Phys. and the Science Abstracts, as the number of the 

 Wien. Ber. containing the original paper could at that time not be found in our Library. 

 In these reviews nothing was mentioned of the method by which a ray tracks had been 

 obtained. When we obtained the original paper afterwards, we found that the method 

 employed by him had, in some ways, been similar to that of ours. However, his lines of 

 investigation were different from ours. 



7) For the case of polonium and of active deposits of thorium, E. R. Sahni's paper in 

 Phil. Mag. 29 (1915), p. 831 may be referred to. 



