ZOOLOGY AND EOT ANY, MICROSCOPY, ETC. 683 



to the manufacture of fine steel, should be used on the ingot immediately 

 after it is cast. It must be borne in mind that while good steel can be 

 spoiled by bad treatment, bad steel cannot be converted into good steel 

 by any kind of treatment except by remelting it. Hence the necessity 

 for immediate examination. 



Simultaneous Presence of Ferrite and Cementite in Steel.* — 

 E. F. Lange has arrived at the conclusion " that there can be no possible 

 donbt, as Mr. Stead says, that structurally free cementite and ferrite 

 may be obtained in the same steel. The conditions favourable to the 

 formation of this structure are an extremely slow cooling between 700° 

 and 600°." In a postscript, A. Sauveur admits the soundness of the 

 conclusion. 



Effect of Superheated Steam upon the Tensile Strength of 

 Alloys.f — J. L. Hall has studied this subject with especial regard to 

 alloys of copper, as experience has quite generally indicated that that 

 metal and some of its alloys have proved unreliable when subjected to 

 the action of highly superheated steam. His experiments point to the 

 conclusion that the tensile strength of bronze is lessened after a first 

 heating and cooling from 320° C, but that subsequent treatment of this 

 nature had little effect upon the ultimate strength. 



Improved Method of Identifying Crystals in Rock Sections by 

 use of Birefringence, and Improved Polarising Vertical Illuminator.^ 

 J. Joly describes a method of observing on an ordinary rock-section 

 the interference tints proper to double the thickness of the section, and 

 of thereby producing discriminative effects not possible to obtain in the 

 ordinary mode of observation. The method consists in placing a plane 

 reflecting surface (polished speculum metal, preferably) beneath the 

 rock-section as it rests on the stage of the Microscope, and transmitting, 

 by means of any vertical illuminator (as used for the examination of 

 metals, &c), a plane polarised ray vertically downwards through the 

 rock-section. The ray reflected from the speculum metal is again re- 

 turned through the object-glass, and, after passing through the analyser, 

 shows to the eye the retardation proper to double the thickness of 

 section. In this manner the range of col our- variation from one species 

 to another is greatly increased ; in fact, what differences exist for the 

 single thickness are now doubled in amount. 



In this method a certain objection applied, in some degree, in all 

 cases — a want of vertically in the downward directed ray, which in- 

 volved necessarily that the section and its images in the reflector did 

 not accurately overlie one another. In rocks of fairly coarse grain this 

 did not signify ; but in those of finer grain, an unpleasant overlapping 

 of the colours of adjacent crystals occurred in the plane of incidence 

 and reflection. In all the forms of the apparatus there was also re- 

 quired a separate polariser to polarise the beam entering the illuminator. 

 The author has found that the simple vertical illuminator described in 

 Messrs. Watson's catalogue gives very satisfactory results. The illu- 



* Metallographist, vi. (1903) pp. 9-13 (1 fig.), 

 t Tom. cit., pp. 3-8 (5 figs."). 



t Sci. Proc. Royal Dublin Soc., ix. (1901) pp. 485-94 (2 figs.) ; x. (1903) pp. 1-5 

 (1 fig)- 



