The apparatus was arranged so that positive ions from a heated Mo strip coated with aluminum phosphate, were accelerated radially through slots in shields $A$ and $B$, and a wider slot in an electrode $C$ to the target $T$, from which the secondary emission to the electrode $C$ was measured. The parts $A$, $B$, $C$ and $T$ were all concentric nickel cylinders, symmetrically placed about the emitter. If the potential of the emitter is made zero and the accelerating potential $V_1$, when the collector is at zero potential only reflected positives are collected. As the potential is increased, secondaries also reach it, the net negative charge increasing until a saturating potential $2V_1$ is reached, when all negatives and no positives are collected. The percentage saturated secondary electron emission was found to increase approximately as the square of the primary ion energy, reaching 22 percent of the primary ion current, for primary ions of energies corresponding to 380 volts. The curves show that large numbers of reflected positive ions have energies between zero and two volts, and there is also a group of reflected positive ions with energies approximately 0.9 of the primary energy.

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