THE METALLOGRAPHY OF METEORIC IRON 



By Stuart H. Perry 



I. INTRODUCTION 



Historical. — Before metallographic methods were applied to the 

 study of meteoric^ iron an extensive Hterature had been built up 

 by the work of a number of able scientists, dealing with their classi- 

 fication, their chemical composition, and such structural features 

 as could be observed at moderate magnification in obhque light. 

 The most famous of those investigators was Cohen, whose Mete- 

 oritenkunde summarized the knowledge upon that subject up to 

 the year 1905. 



Their researches, however, were limited by the imperfect methods 

 then available; for the ordinary microscope at best could reveal 

 only the coarser contrasts in structure. The invention of vertical 

 illumination opened a field of research that not only laid a new foun- 

 dation for metallurgy but also greatly extended our knowledge of 

 meteoric iron. 



Vertical illumination was invented perhaps as early as 1865, and 

 the illuminator in substantially its present form was described in 

 the 1883 edition of W. B. Carpenter's book "The Microscope." It 

 was used for a number of years by Sorby, whose description of the 

 microstructure of iron and steel (1887) was the most important 

 early contribution to that subject. 



Its application to the study of meteoric iron, however, was singu- 

 larly tardy. Although Cohen (1894) cited Sorby 's work, and several 

 others dealing with the microstructure of metals, and (1903) men- 

 tioned Reichert's new "metal microscope," which he said made 

 possible photomicrographs up to a magnification of 200 diameters, 

 he apparently made no use of the device, and his works are silent on 

 the finer microstructure of meteoric iron. It was not until 15 years 

 later that Pfann (1917) and Berwerth (1918) published the first 

 discussions of such structures with photomicrographs, the result of 

 studies made with a Reichert microscope that had become available 

 in Vienna. Even so, until in quite recent years, scientists continued 

 to describe and discuss iron meteorites in the language of the older 

 writers. Nevertheless, while metallography has opened up a new and 



1 The terms meteor and meteorite are clearly distinguished, the former being applied to the body while 

 in flight, the latter to such portion of it as reaches the earth. Similarly, a distinction is drawn between the 

 words meteoric and meteoritic. In this work the author uses the term meteoric iron because its composi- 

 tion and structure were established while the mass was a meteor. In a few instances the word meteoritic 

 is used in referring specifically to meteorites, or to some structure that developed in a meteorite after its 

 fall. 



1 



