Progress on the design and development of an electronic x-ray microprobe for quantitative and qualitative composition measurements of about 1 cubic micron of the surface of metals and alloys is described in this report. The principle is that first used by Castaing, in which the metal is subjected to bombardment by a finely focused probe of electrons and the elements present and their proportions are determined by an analysis of the frequency and intensity of the characteristic x-rays emitted. With the first model of the instrument, it will be possible to study the elements in the ranges of atomic numbers 19 through 34 and 50 through 84. This report omits any theoretical treatment of the effects of heat generated in the sample...