The Microscopy of Metals

Abstract

AT the very successful symposium on the microscope organised by the Faraday Society on January 14 in the rooms of the Royal Society, about one-half of the papers presented dealt with the microscopical examination of metals, a striking indication of the importance which this branch of microscopy has now acquired. It was therefore appropriate that the president, himself a distinguished worker in this field, should deal historically with the development of micro-metallography, as well as contributing an original paper to the discussion. Sir Robert Hadfield's introductory address surveyed the history of microscopical in vention, and was illustrated by portraits of some of the pioneers in the art-Jansen, Lipperhey, Leeuwenhoek, Sorbyr and Dallinger. We were reminded of the fact that, so far back as 1665, Robert Hooke described, in his “Micrographia” the appearance of the point of a needle and the edge of a razor, and his faithful drawings of these two objects, revealing most accurately the features which could be observed under a low magnifica tion, are reproduced in the paper. The next in stance of the application of the microscope to the examination of metals is that by Réaumur, whose work on steel, published in 1722, contains many drawings of the magnified fractures of iron and steel bars. Such a method, however, gave little information, and did not lead to any further development. In 1808 Widmanstatten studied the structure of meteoric irons by polishing a plane section and heating until the constituents became differentially coloured by oxidation, thus introduc ing the method now familiar as “heat-tinting.” The structure of these irons is so coarse that mag nification is unnecessary, but the method gave hints to later workers, of whom Sorby is the chief. The work of Sorby, in view of its great importance, was dealt with by the president in a separate note.