00000047.htm

36 RAYS OF POSITIVE ELECTRICITY

V it would not get ionized. Hence the velocity of the
secondaries we are considering must be very approximately
equal to V, a velocity which depends only on the nature of
the particle and not on the potential difference applied to the
discharged tube. This accounts for the fact that the velocities
of the particles forming the secondary rays are independent of
the potential difference between the anode and cathode.

We can by the method described on page 12 measure the
velocity of the particles In the secondary rays corresponding
to any atom and hence determine V, the smallest velocity
which a corpuscle can have if It Is to be able to ionize the atom.
When this method Is applied to the secondary rays connected
with the hydrogen atom we find that V is about 2 x I o⁸ cm./sec.
This velocity would be acquired by a corpuscle if it fell through
a potential difference of 11 volts. Hence we may take 11 volts
as the measure of the energy required to ionize an atom of
hydrogen.

To give to the atom of hydrogen this velocity requires a
potential difference of 11 x 1*78 x io⁷/io⁴ volts (taking e/m
for the corpuscle to be 178 x >io^r and for the atom io⁴), this
Is about 20,000 volts. If it required the same energy to ionize
an atom of oxygen as one of hydrogen, V would be the same
for oxygen as for hydrogen. To give an atom of oxygen this
velocity would require a potential difference of 16 x 20,000, or
320,000 volts, a much greater potential difference than we
usually apply to the discharge tubes. Thus we see that we can-
not expect any except the lighter gases such as hydrogen or
helium to show secondaries of the type we are considering.

There Is, however, another type of secondary—that due to
particles which enter the magnetic field in a charged state and
lose their charge before emerging from It: this type of second-
ary, since It arises from the combination of a positively charged
particle with a negatively charged corpuscle, might be expected



	36 RAYS OF POSITIVE ELECTRICITY V it would not get ionized. Hence the velocity of the secondaries we are considering must be very approximately equal to V, a velocity which depends only on the nature of the particle and not on the potential difference applied to the discharged tube. This accounts for the fact that the velocities of the particles forming the secondary rays are independent of the potential difference between the anode and cathode. We can by the method described on page 12 measure the velocity of the particles In the secondary rays corresponding to any atom and hence determine V, the smallest velocity which a corpuscle can have if It Is to be able to ionize the atom. When this method Is applied to the secondary rays connected with the hydrogen atom we find that V is about 2 x I o⁸ cm./sec. This velocity would be acquired by a corpuscle if it fell through a potential difference of 11 volts. Hence we may take 11 volts as the measure of the energy required to ionize an atom of hydrogen. To give to the atom of hydrogen this velocity requires a potential difference of 11 x 1*78 x io⁷/io⁴ volts (taking e/m for the corpuscle to be 178 x >io^r and for the atom io⁴), this Is about 20,000 volts. If it required the same energy to ionize an atom of oxygen as one of hydrogen, V would be the same for oxygen as for hydrogen. To give an atom of oxygen this velocity would require a potential difference of 16 x 20,000, or 320,000 volts, a much greater potential difference than we usually apply to the discharge tubes. Thus we see that we can- not expect any except the lighter gases such as hydrogen or helium to show secondaries of the type we are considering. There Is, however, another type of secondary—that due to particles which enter the magnetic field in a charged state and lose their charge before emerging from It: this type of second- ary, since It arises from the combination of a positively charged particle with a negatively charged corpuscle, might be expected