1. Preliminary results were presented at the C.A.P. Congress,1972
2. Also see Phys. in Canada 28, Abstract EB12.
3. As we were preparing this paper, we were informed of the results of low energy resolution experiments on Cu, Au and Al by P.G. Coleman et al., Proc. Roy. Soc., to be published.
4. Supplied through the courtesy of the Bendix Corporation, Electro-Optics Division.
5. Evidence for the Negative Work Function Associated with Positrons in Gold