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222 RAYS OF POSITIVE ELECTRICITY

has shown that magnesium atomic weight 24 has elements
26, 29 as companions (Proa Nat Ac., Wash, 7, p. 45, 1921).
The relative intensities of the lithium lines 6 and 7 have been
found both by Thomson and Dempster to be very variable.

The method of analysing a gas by superposed magnetic
and electric fields can be applied to cases other than those in
which the ions are positive rays streaming through a hole
in the cathode. It can be applied, for example, to investi-
gate the nature of the ions in the electric arc, in the positive
column of a discharge through a gas at low pressure, the ions
produced in flames, and so on. In these cases the ions
have not in general sufficient energy to affect a photographic
plate, so that it is necessary to accelerate them before they
reach the plate. To do this the ions are produced in a vessel
A, which is connected by a very narrow channel with another
vessel B, in which a high vacuum is maintained. The gases
from A rush through the channel into B, when they at once
pass through two parallel pieces of wire gauze, between
which there is a potential difference of several thousand volts
obtained by connecting them with the poles of a small
Wimshurst electrical machine, a spark a few millimetres long
passing between the poles* The field between the gauzes
accelerates the ions of one sign and gives them energy enough
,to affect the photographic plate which they reach after passing
through the usual electric and magnetic fields,

The method of positive rays enables us to apply searching
tests to theories of the constitution of the atom and the
structure of molecules. Thus for example on one theory
the atoms of the elements are made up of electrons and one
positive charge, the positive charge being at the centre and
the electrons distributed around it. The negative electricity
on the electrons is equal in magnitude to the positive
electricity on the positive charge. The atoms of the different



	222 RAYS OF POSITIVE ELECTRICITY has shown that magnesium atomic weight 24 has elements 26, 29 as companions (Proa Nat Ac., Wash, 7, p. 45, 1921). The relative intensities of the lithium lines 6 and 7 have been found both by Thomson and Dempster to be very variable. The method of analysing a gas by superposed magnetic and electric fields can be applied to cases other than those in which the ions are positive rays streaming through a hole in the cathode. It can be applied, for example, to investi- gate the nature of the ions in the electric arc, in the positive column of a discharge through a gas at low pressure, the ions produced in flames, and so on. In these cases the ions have not in general sufficient energy to affect a photographic plate, so that it is necessary to accelerate them before they reach the plate. To do this the ions are produced in a vessel A, which is connected by a very narrow channel with another vessel B, in which a high vacuum is maintained. The gases from A rush through the channel into B, when they at once pass through two parallel pieces of wire gauze, between which there is a potential difference of several thousand volts obtained by connecting them with the poles of a small Wimshurst electrical machine, a spark a few millimetres long passing between the poles* The field between the gauzes accelerates the ions of one sign and gives them energy enough ,to affect the photographic plate which they reach after passing through the usual electric and magnetic fields, The method of positive rays enables us to apply searching tests to theories of the constitution of the atom and the structure of molecules. Thus for example on one theory the atoms of the elements are made up of electrons and one positive charge, the positive charge being at the centre and the electrons distributed around it. The negative electricity on the electrons is equal in magnitude to the positive electricity on the positive charge. The atoms of the different