-particles do not penetrate the air after the manner of a bullet, namely, by pushing the molecules of air aside, but rather that they actually shoot through all the molecules of air which they encounter. The number of such passages through molecules which an
-particle would have to make in traversing seven centimeters of air would be about a hundred and thirty thousand.
Further, the very rapid
-particles, or negative electrons, which are shot out by radium have been known for a still longer time to shoot in straight lines through much greater distances in air than 7 cm., and even to pass practically undeflected through appreciable thicknesses of glass or metal.
We saw in [chap. VI] that the tracks of both the
- and the