276 



NATURE 



[June 5, 1919 



(mechanical, musical, or electrical) were thus rendered 

 simultaneously visible. 



The National Physical Laboratory: Mechanical and 

 optical apparatus for measuring and inspecting screw 

 gauges (Metrology Department). A vertical projec- 

 tion machine shown produces an enlarged image of 

 the profile of the thread on a diametral plane to a 

 magnification of 50. This image can be compared 

 with the standard form for the thread which is drawn 

 out to the same magnification. Errors of ooooi" in 

 the thread-form can be so detected. 



Mr. A. Mallock: Apparatus used in the measure- 

 ment of the growth of trees. An ''invar" tape was 

 passed round the tree and over the "rockers" on the 

 apparatus, the arms of which control the angle be- 

 tween a plane glass surface and the face of a right- 

 angled glass prism. The growth of the tree con- 

 tinually alters this angle, the variation of which was 

 measured by observing the change of position of the 

 interference bands formed, at grazing incidence, be- 

 tween the plane and prism. The details of the pro- 

 cedure are given in Proc. R.S., vol. xc. B, 1918, p. 186 

 et seq. 



Prof. Ernest Wilson: Instruments for measuring 

 minute susceptibilities, including a portable instru- 

 ment for survey work. The action of the instrument 

 depends upon the mechanical force exerted by a mag- 

 netic field on a magnetic material placed in it, the 

 force per unit volume being proportional to the 

 gradient of the square of the field. It is ultimately 

 measured by a galvanometric method involving the 

 action of a spot of light, except in the case of the 

 portable instrument, when a pointer is more con- 

 venient. 



The National Physical Laboratory: (i) Apparatus 

 for the determination of the absolute viscosities of 

 liquids at high pressures. (Designed by Mr. J. H. 

 Hyde ; method • suggested by Dr. T. E. Stanton.) 

 The apparatus consists essentially of a system of two 

 horizontal (the upper one of capillary dimensions) and 

 two vertical tubes forming a closed circuit of liquid 

 under pressure, the lower half of the circuit contain- 

 ing mercury and the upper half the liquid under test. 

 The system rests on a horizontal knife-edge, and is 

 supported in a horizontal position by a spiral spring. 

 On the mercury being displaced by a given amount, 

 flow will take place round the circuit owing to the 

 difference of head, and if the spring is so adjusted 

 that its rate of extension is equal to the rate of change 

 of head of the mercury, it is evident that flow of the 

 liquid under test will take place through the capillary 

 under a constant-pressure difference, and at a velocity 

 which can be calculated from the rate of extension of 

 the spring. (2) Three-electrode vacuum tube with 

 circuits arranged to produce oscillations of telephone 

 frequency. (Mr. F. E. Smith.) The apparatus con- 

 sists of a three-electrode vacuum tube with appro- 

 priate inductances and capacities in the plate- and 

 grid-circuits. The values of these are such as to 

 maintain oscillations of audible frequency. By vary- 

 ing either inductance or capacity the frequency of the 

 oscillations is varied. A coil coupled to the plate 

 inductance with a telephone in circuit serves to make 

 the note audible. By suitably choosing the induct- 

 ances and capacities, freouencies from about twenty 

 per second to several millions per second are readily 

 obtained, (t.) Plottinrf chronos?raph, thermal curves, 

 and model relating to ternary alloys. (Dr. W. Rosen- 

 hain.) The chronograph was designed for the direct 

 plotting of time-temperature observations in the form 

 of "inverse rate " curves as required for the heating 

 and coolin J? .curves of metals and alloys. The con- 

 stitution of a binarv allov svstem can be completely 

 represented by a plane diagram, but for a ternary 



NO. 2588, VOL. 103] 



system a three-dimensional model is required. The 

 model shown indicated the constitution of a part of 

 the system zinc-copper-aluminium, including alloys 

 rich in zinc, and containing up to 10 per cent, of 

 copper and 15 per cent, of zinc. 



Sir Robert Hadfield : Stereoscopic radiographs of 

 large carbon electrodes. These electrodes are used in 

 electric steel-smelting furnaces, the largest type being 

 no less than 22 in. in diameter. For effective and 

 economical working of the furnaces it is essential that 

 the electrodes do not break and fall into the bath. 

 The finer the structure of the electrode and the fewer 

 the inclusions, the less does the possibility of breakage 

 arise. The stereoscope showed four different types of 

 electrodes which are largely used. 



Major G. W. C. Kaye and Dr. R. Knox: The 

 detection of defects in aeroplane timber by the X-rays. 

 The best workmanship and the highest quality 

 material are essential in aircraft construction. The 

 X-rays readily reveal bad workmanship and hidden 

 defects in the interior of lam.inated or box spars and 

 struts which cannot be seen by ordinary visual 

 examination. As wood is very transparent to X-rays 

 the fluorescent-screen method of examination suffices 

 for routine inspection. 



The Munitions Inventions Department : War re- 

 search on nitrogen fixation. For the past three years 

 the research laboratory of the Munitions Inventions 

 Department, constituted under the auspices of the 

 Nitrogen Products Committee of the Ministry of 

 Munitions, has been conducting experimental in- 

 vestigations on various methods for the fixation of 

 nitrogen. The most important divisions of the work 

 have been concerned with the synthesis of ammonia, 

 the oxidation of ammonia and the preparation of 

 nitrates, and the preparation and purification of 

 hydrogen. Experiments illustrative of the work of 

 three of the sections are shown. 



Mr. A. Chaston Chapman: "Mineral yeast," used 

 in Germany during the war for human food. The 

 organism exhibited is very similar to, if not identical 

 with, the so-called "mineral yeast" which was manu- 

 factured in Germany in considerable quantities during 

 the war and used to supplement the bread ration. 

 The organism is not a true yeast — that is to say, it 

 does not belong to the genus Saccharomyces. It 

 grows freelv upon nutrient solutions at a temperature 

 of 38°-40° C., forming a thick, greasy, crinkled film. 

 It does not produce alcohol, and the time needed for 

 a full crop is about thirty-six to forty-eight hours. 

 The separated organism contains 50-55 per cent, of 

 protein and about 5 per cent, of fat, expressed on 

 the moisture-free m'aterial. It is entirely free^ from 

 bitterness and has a pleasant flavour, suggestive of 

 that of cream cheese. As a source of carbon, glucose 

 or molasses answer well, and the organism is capable 

 of supplying the whole of its nitrogen needs from 

 ammonium salts — that is to say. it does not require 

 anv organic nitrogen. In addition to the above, 

 phosphates must be present, and small quantities of 

 potassium and magnesium salts. 



Mr. J. E. Barnard : Methods of observing Spiro- 

 chaetes bv dark-ground illumination. It is recognised 

 that for the identification of Spirochaetes, particularly 

 Si)ironema ■hallidum. the method of microscopical 

 observation known as dark-ground illumination is the 

 most satisfactorv. To employ it successfully certain 

 optical principles must be complied with. Such 

 organisms are alwavs within the limits of micro- 

 scopic resolution in the direction of their length, but 

 are often bevond the limits in breadth. It follows 

 that any granular contents are ultra-microscopic, and 

 that these are seen onlv under certain conditions. 



Dr. R. T. Leiper : Demonstration illustrating the 



