-particles through air could be photographed because they ionize some of the molecules through which they pass. These ions then have the property of condensing water vapor about themselves, so that water droplets are formed which can be photographed by virtue of the light which they reflect. [Fig. 17] shows the track of a very high-speed
-ray. A little to the right of the middle of the photograph a straight line can be drawn from bottom to top which will pass through a dozen or so of pairs of specks. These specks are the water droplets formed about the ions which were produced at these points.
Fig. 14—Photographs of the Tracks of
-Particles Shooting through Air
Fig. 15—Photographs of the Tracks of