Fig. 2. — Tni 



electrons (C. T. R. Wilson). Note that the tracks are dotted and irregular 



P'iG. 3a. — ( Fig. 2,l> shows how to find the track of a positive electron in this figure.) Tracks of 

 positive helium atoms, and a track of the positive electron (proton or nucleus [H+] of the hydrogen 

 atom). This photograph illustrates the synthesis of an atom, since a helium atom strikes a nitrogen 

 atom and forms a (heavier) o.xygen atom and a hydrogen atom. (Photograph by Harkins and 

 Shadduck.) 



