Joseph John Thomson

“ If b is the length of the plates measured parallel to the axis of x, and if one end of the plates just comes up to the point from which the particle is projected, putting Z=Z from x=0 to x=b, and Z=0 from
x= b to x=l, we find that
so that If z is the deflection when x=l
The electric field Is not absolutely constant between the plates, It is greater close to the edges than in other parts of the field, nor it absolutely vanish at all places outside the plates ”

“ Thus y/z will be constant for all particles moving with a given speed whatever may be their charge or mass, hence all such particles will strike the screen in a straight line passing through the undeflected position of the particles. ”