of [Fig. 33] and a beam of monochromatic light from a spectrometer was let in through
and allowed to fall on the new surface. The energy of the electrons ejected by it was measured by applying to the surface a positive potential just strong enough to prevent any of the discharged electrons from reaching the gauze cylinder opposite (shown in dotted lines) and thus communicating an observable negative charge to the quadrant electrometer which was attached to this gauze cylinder.
Fig. 33
For a complete test of the equation it was necessary also to measure the contact-electromotive force between the new surface and a test plate
. This was done by another electromagnetic device shown in [Fig. 32], but for further details the original paper may be consulted.[168] Suffice it here to say that Einstein’s equation demands a linear relation between the applied positive volts and the frequency of the light, and it also demands that the slope of this line should be exactly equal to
