ELECTRIC RADIATIONS—BRAGG. 205 
Having thus discussed certain properties of the various rays which 
do exist, it seems interesting to make an attempt at the estimation 
of the properties of some rays which might exist, though the fact has 
not been proved as yet. Radioactive substances emit both positive 
and negative particles. It does not seem at all out of place to con- 
sider the possibility of the emission of neutral particles, such as, for 
example, a pair consisting of one a or positive particle and one B or 
negative particle. The recent additions to our knowledge of the 
laws of absorption of a and B particles give us some grounds on 
which we may attempt to found an estimate of the properties of 
such pairs. 
We know that the a particle moves in a rectilinear course through- 
out its whole range, and passes through the atoms which it encounters 
without deflection. It does not pursue a course which is straight 
on the whole, but zigzag in detail; the direction and amount of a 
particle in motion are the whole characteristics of that motion at any 
instant, and no memory of any previous motion exists. If, there- 
fore, a particle pursues a straight line in its motion as a whole, it 
must keep to that line entirely and make no excursions from side to 
side. We must, therefore, suppose that an atom, or at least an a 
particle, endowed with sufficient speed, can pass directly through 
another atom without appreciable deflection. The a particle loses 
speed as it penetrates atoms in this way; and there can be little doubt 
that its charge, that is to say, the field which is about it, is a main 
cause of this loss of energy. But if a 8 particle is associated with 
the a particle so that the tubes of induction pass from one particle to 
the other, and the field is greatly contracted, it would seem that the 
chief cause of the stopping of the a particle has been removed.* The 
penetrating power of a pair might be very great indeed, and its 
lonizing power correspondingly reduced; for, although there does 
not seem to be a direct connection between energy spent and loniza- 
tion produced, there can be no doubt that the two are simultaneous. 
The limitation of the field of the pair would depend on its moment; 
if the latter were small, that is to say, if the positive and negative 
were close together, the field would be more circumscribed. It is, 
therefore, possible to provide for pairs to have varying penetrating 
and ionizing powers; a pair of small moment being a good pene- 
trator but a bad ionizer. Such a pair would be incapable of deflection 
by magnetic or electric fields, and would show no refraction. It 
is conceivable that it might show a one-sided or polarization effect, 
for if it were ejected from a rotating atom it would itself possess an 
axis of rotation. 
@ See also Rutherford’s ‘* Radioactive Transformations,” p. 272. 
