322 SUMMARY OF CURRENT RESEARCHES. 



red light reflected upwards from the inner concave surface of the pit, 

 thus demonstrating the transparence of the film and the emptiness of 

 the pit when covered by the him. The thickness of the films covering 

 the pits is probably of the order of 10 to 20 micro-millimetres. Repro- 

 ductions by the three-colour process of autochrome photomicrographs at 

 magnifications of 800 and 1800 diameters illustrate the paper. 



Microscopic Metallography in Three Dimensions.* — A. Portevin 

 describes the apparatus he has devised for studying the solid structure 

 of metal specimens by the histological method of serial sections. The 

 piece to be examined is permanently fixed, by means of gum-lac or 

 other cement, in a specimen-holder, which is an accurately turned hollow 

 steel cylinder. The holder fits into a recess in a bronze base-plate, which 

 fits in turn into the stage opening of the Le Chatelier Microscope. The 

 stage, base-plate, and specimen holder bear register marks, which are 

 made to coincide when the specimen is re-examined after each successive 

 polishing. The accurate replacement of the specimen in the same 

 position in space with respect to the Microscope stage, thus, rendered 

 possible, permits the re- examination of any field, after removal of a 

 layer of known thickness, by means of recorded readings of the micro- 

 meter heads of the mechanical stage. The thickness of the layers suc- 

 cessively removed by re-polishing is determined by measuring the length 

 of the specimen-holder, after each polishing, by means of a micrometer 

 calliper with anvil of large diameter. In polishing, care must be taken 

 to maintain the face accurately at right angles to the axis of the specimen- 

 holder. A number of serial photomicrographs are given, of an antimony- 

 tin-copper-lead bearing metal, and a copper-tin alloy, the distance between 

 the successive parallel faces varying from 0*05 to " 12 mm. 



Cohesion of Metal Masses.!— W. Guertler agrees with Rosenhain's 

 amorphous cement theory, provided that the thickness of the amorphous 

 layers is not assumed to exceed molecular dimensions. The existence 

 of independently stable amorphous masses is disputed, chiefly on the 

 ground of the higher stability of the crystalline state. 



Colour-photomicrographs of Ores 4 — Gr. Rigg has found Lumiere 

 autochrome photomicrographs useful for recording the microstructure 

 of thin slices of ores illuminated by transmitted light. The fineness 

 of the constituents, the shape of the different minerals, and the mode of 

 association of the valuable minerals with the gangue, are revealed by 

 microscopic examination. 



* Int. Zeitschr. Metallographie, vi. (1914) pp. 58-71 (35 figs.), 

 t Int. Zeitschr. Metallographie, v. (1911) pp. 213-27 (2 figs.). 

 X Met. and Chem. Eng., xii. (1914) p. 30. 



