s«>\// COM I uroh'.iKv inrixcis i\ riiysits in ,iji 



priHi-i-tl tlii'DUKii .lir Mii)i'i>.iliir.iif«l willi w.id-r vapor, shows f\i(lciu-e 

 lor ilu'sc.'* 'V\\v long sinuous trails an- those of fast i-IiTtrons, which 

 wiri' liht-ralfd from their atoms l>\ hinli-fre(iuen(>- (jnanta proceeding 

 across the gas; each of these electrons possesses the entire energy 

 of a \ai)islu'i| ((uantuni (minus sue!) |>arl of it .1^ w.i^ v^irriticci! when 



l-ig. II — Trails of rciMiillng C'livlrons (C.T. R. Wilson, Proreeiliiie,s of Ihe Royiit Society) 



the electron emerged from its atoni). The small sligliilv -clotigated 

 comma-like "blobs", the "fish tracks" as t\ '1'. R. Wilson called 

 them, are the trails of very slow electrons — these are the electrons 

 from which quanta rebounded, transferring in the reboimd a little of 

 their energy and a little of their momentum. These appear only when 

 the frequency of the X-ray quanta exceeds a certain minimum amount 

 — a circumstance which, combined with others, shows that the com- 



'• I am inilcl)tc<l to Professor C. T. R. Wilson and to the Si-crctary of the Royal 

 Society for permission to repriKluce these photographs. 



