ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
221 
Determination of Optic Axes from Extinction Angles. — Ii. Hilton 
{Miner alogical Soc ., Nov. 1, 1921). By using the extinction-directions 
on four known faces of a crystal the position of the optic axis is 
obtained. From a geometrical standpoint the solution is shown to be 
unique. F. I. G. R. 
METALLOGRAPHY, Etc. 
Electro-deposited Iron and Effect of Acid. — W. E. Hughes 
{Trans. Faraday Soc., 1922, 17, Part 2). After giving details of the 
method of electro-deposition, the author proceeds to the microstructure 
of the deposit. He gives a remarkable photomicrograph showing the 
appearance during the two periods considered ; also the effect, under 
very high magnification, of the characteristic copper film. Two types 
of structure are recognized, “ normal ” and “ fibrous,” and the con- 
nexion between them is traced, An illustration of the influence of acid 
concludes the paper. F. I. G. R. 
High Temperature Phenomena of Tungsten Filaments. — C. J. 
Smithells and Others {Trans. Faraday Soc., 1922, 17, Part 2). 
Two types of tungsten wire are used for lamp filaments — (1) Pure 
tungsten ; (2) tungsten + refractory oxide. The deformation of the 
filament is found to be a function of crystal growth. Numerous photo- 
micrographs accompany the paper. F. I. G. R. 
Recrystallization of Cu-Zn Alpha Solid Solution. — M. Cook 
{Trans. Faraday Soc., 1922, 17, Part 2). The author describes the 
behaviour of an unworked alpha brass, containing 30 p.c. Zn, 70 p.c. 
Cu. An interesting photomicrograph shows that twin crystals can be 
produced in a casting annealed at 825° C., no previous work having 
been done upon the specimen. F. I. G. R. 
Inner Structure of Pearlite Grain. — N. T. Belaiew (Iron and 
Steel Institute Meeting, May, 1922). The author sets out to investi- 
gate a series of iron-carbon alloys, subjecting them to extremely slow 
rates of cooling. By this means he develops the pearlite to as coarse 
a degree as possible ; in some cases this constituent is relatively so 
large as to be visible with a magnification of 30 to 50 diameters. Many 
workers have noticed the peculiarity that the fineness of the pearlite 
varies considerably in different crystal grains of the same sample. This 
paper endeavours to show how the appearance of pearlite is influenced 
by the direction in which the section is made. Data (and some very 
interesting illustrations) are given for a number of different angles of 
inclination. The author also gives the results of his micrometric observa- 
tions on the width of the lamellae. Following Prof. Arnold much 
stress is laid on a correct understanding of the “ solid geometry ” of 
steel. F. I. G. R. 
