of the start pulse in time of arrival correlators," Rev. Sci. lnstrum. 60, 634-637 (1989). 2 £Tor reasons of electronic simplicity, the delay is made to correspond to a number of pulses that is a power of 2.

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The critical-field theory of electrical breakdown in vacuum is shown to be applicable to all of the twelve metals and to the one alloy tested. In this theory the electric field at breakdown is predicted to be independent of gap spacing when the field considered is that existing in the neighborhood of cathode field-emission sites. This field is enhanced with respect to the average gap field by a factor which can be calculated from measurements of the field-emission current prior to breakdown. A vacuum tube has been employed for the experiment in which one electrode is movable and in which foils may be used for the electrode materials. The critical field for breakdown compares well with that calculated by others in the four metals for which previous data exist.

A little-known integral formulation, of considerable simplicity, has been used to" compute" representative values of the average solid angle subtended at a disk source by a coaxial parallel-disk detector. The advantage of the integral formulation is compared with a Monte Carlo calculation of the solid angle. It is concluded that the Monte Carlo calculation is of lesser advantage, but is more easily adaptable to complex geometries.