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THE PHOTOGRAPHS 29

Let us now consider the case of the charged particles which
get neutralized while passing through the field. The part of
the line near the origin will be due to particles which get
neutralised almost as soon as they enter the field. We have
supposed that the magnet was moved towards the camera so
that its field overlapped the electric on that side. This will
tend to make the electric field overlap the magnetic on the other
side, i.e. the side nearest the cathode, so that when a particle
first enters the field Its deflection is mainly due to the electro-
static force and is therefore horizontal; thus a particle which
gets neutralized at the early stages of Its journey through the

FIG. 18. FIG. 20,

fields will have a horizontal displacement abnormally large
compared with the vertical; so that the curves produced on the
photographic plate by the particles which get neutralized will
have a shape something like that shown in Fig. 20. We see
that with these overlapping fields we can distinguish between
the lines which are due to particles which have gained a charge
in their journey and those which have lost one. The concavi-
ties of the two curves are in opposite directions. These two
sets of lines are very prominent In photographs taken with
apparatus in which care has not been taken to make the fields
coterminous; an example of this Is shown in Fig. 19, Plate I.



	THE PHOTOGRAPHS 29 Let us now consider the case of the charged particles which get neutralized while passing through the field. The part of the line near the origin will be due to particles which get neutralised almost as soon as they enter the field. We have supposed that the magnet was moved towards the camera so that its field overlapped the electric on that side. This will tend to make the electric field overlap the magnetic on the other side, i.e. the side nearest the cathode, so that when a particle first enters the field Its deflection is mainly due to the electro- static force and is therefore horizontal; thus a particle which gets neutralized at the early stages of Its journey through the



	FIG. 18. FIG. 20, fields will have a horizontal displacement abnormally large compared with the vertical; so that the curves produced on the photographic plate by the particles which get neutralized will have a shape something like that shown in Fig. 20. We see that with these overlapping fields we can distinguish between the lines which are due to particles which have gained a charge in their journey and those which have lost one. The concavi- ties of the two curves are in opposite directions. These two sets of lines are very prominent In photographs taken with apparatus in which care has not been taken to make the fields coterminous; an example of this Is shown in Fig. 19, Plate I.