NEGATIVELY CHARGED PARTICLES 4*
atoms quite comparable'in intensity with those due to the posi-
tive ones.
Though in one sense all the lines due to negatively charged
particles are secondaries they show differences amongst them-
selves corresponding to the difference between the primary and
secondary positive lines. Some of the negative lines like the
positive secondaries come close up to the origin, while there
are others which, like the primary positives, are finite arcs of
parabolas, terminating abruptly when they approach within
a certain distance of the vertical axis. Indeed the lines on the
negative side are frequently exact reproductions in shape and
size of the corresponding lines on the positive. An example of
this is shown in Fig. 26, Plate II., where the curves a and jS are
the lines corresponding respectively to the positively and nega-
tively electrified atoms of oxygen when the discharge passed
through very pure oxygen: it will be seen that every detail in
the positive curve is reproduced in the negative. This might
suggest that the positive and negative atoms were the two
halves of a neutral molecule which divided after passing
through the cathode. Further consideration, however, shows
that this view is not tenable, at any rate in the great majority
of cases. The heads of the negative parabolas, like those of the
positive, are all on a vertical line and the distance of this line
from the vertical line through the origin is about the same as the
corresponding distance for the positive parabolas. From this
it follows by equation (2) (p. 12) that the maximum value of
\mv^\e is the same for the negative as for the positive particles
and equal to the potential difference between the anode and
cathode of the discharge 'tube. To take a definite case, let us
suppose that the negatively charged hydrogen atom owes its
charge to having been in chemical combination with an atom
of carbon before it passed through the cathode, the molecule
of the compound being positively charged when in the discharge