July 7, 1921] 



NATURE 



595 



There were also shown in this department 

 exhibits illustrating the macro-structure ot cast- 

 ings in various types of moulds, graphite moulds 

 and ingots cast in them'; specimens illustrating the 

 behaviour of pure zinc under tensile tests at vari- 

 ous temperatures, and new apparatus for the 

 pressure casting of china clay pots for glass melt- 



In the heat division of the physics department 

 two novel forms of optical pyrometer were shown, 

 one a precision laboratory standard, and the other 

 a portable instrument suitable for workshop use. 

 Both were of the disappearing filament type 'in 

 which an image of the hot object is superimposed 

 on the filament of the pyrometer lamp and the 

 brightness matched by varying the current 

 through the lamp. In the standard instrument 

 two lamps are fitted which can be interchanged 

 exactly in the field by a simple transverse motion, 

 and each lamp is provided with fine adjustment in 

 three mutually perpendicular planes. The portable 

 instrument is a self-contained unit which can be 

 carried in the pocket. The telescope, variable 

 rheostat, and ammeter are integral parts of the 

 instrument, and the ammeter is graduated to read 

 temperatures direct. 



.A variety of hygrometers was shown, as were 

 also appliances for the rapid calibration of these 

 instruments. Considerable modifications have 

 been made in the dew-point apparatus with the 

 view of arranging it in a form suitable for use 

 under cold storage conditions. 



In the radiology division was shown a Bragg 

 X-ray spectrometer for the investigation of the 

 crystal structure of materials. The spectrometer 

 is also designed to measure accurately the absorp- 

 tion of X-rays of definite wave-length in different 

 substances. The whole of the high-tension circuit 

 is enclosed in a box covered with lead, so that the 

 measuring instruments are entirely protected from 

 stray radiation. The apparatus employed to 

 investigate the measurement of the intensity of 

 a beam of X-rays with special reference to the 

 barium platinocyanide pastille was shown, and an 

 improved type of tintometer for comparing the 

 tints of pastilles was also demonstrated. 



The optical division showed a new method for 

 determining loss of light in optical instruments 

 such as range-finders, periscopes, etc. An optical 

 pyrometer, adapted for use as a surface bright- 

 ness photometer, is employed to measure the 

 brightness of a suitable source of light and of its 

 image formed by the optical instrument. Two 

 precision methods of goniometry by substitution 

 were demonstrated. In one of these an accuracy 

 of about i" of angle is readily obtained, and 

 in the other, which is suitable onlv for very accu- 

 rately worked prisms, it is hoped to attain an 

 accuracy of a small fraction of a second. Among I 

 the other exhibits were an improved Lovibond 

 colorimeter, various instruments for measurements 

 of focal lengths and curvatures, and an interfer- 

 ence test of the surface of glycerine showing that 

 such a surface, even when left undisturbed for 

 many weeks, does not become flat. 

 XO. 2697, VOL. 107] 



The metrology department demonstrated 

 optical tests on the flat faces of end gauges for 

 determining flatness, parallelism, and squareness 

 to axis of gauge. An optical proof plane is held 

 opposite one end of the gauge and rotated 

 about two perpendicular axes lying in its own 

 plane. The appearance of the interference fringes 

 formed between the proof plane and the end face 

 of the gauge gives an indication of the state of 

 perfection of the flatness of the face. By observ- 

 ing any change in the interference pattern as the 

 gauge rotates about its own axis, the test of 

 squareness of the face to the axis is obtained. 

 The method of testing the^ flatness of a large sur- 

 face consists essentially of the comparison of the 

 surface to be tested with the horizontal free 

 surface of mercury. 



Other exhibits in this department were a 

 standard leading screw lathe, line standards, and 

 a method of determining the length of an end 

 gauge with reference to a standard scale. 



In the William Froude national tank experi- 

 ments were conducted in connection with the 

 manoeuvring power of ships. The experiments 

 may be divided into two main sections, the action 

 of the water on the rudder of a ship, which will 

 vary with ship form features, type of rudder, etc., 

 and the action of the rudder forces on the ship 

 as a whole. Measurements are taken of the water 

 moments on the rudder stock and on a second axis 

 of the rudder, with and without propeller working, 

 and of the. initial torque on the hull, with the 

 rudder over to any angle. 



The photometry division of the electricitv de- 

 partment showed a method of determining the 

 distribution of light from the lenses used in ships' 

 navigation lights. .Apparatus was also shown for 

 the polar distribution of light. This is of the 

 ordinary two-mirror form, but with special 

 arrangements for the ready rotation of the mirror, 

 the holders for which rotate on ball bearings. 

 .Another exhibit was the integrating sphere photo- 

 meter. This is an Ulbricht sphere of i metre 

 internal diameter, which has been designed for 

 the measurement of lamps of ordinarv com- 

 mercial sizes. 



The exhibits in the wireless division included 

 closed-coil wireless direction-finding systems. 

 The particular coil exhibited was designed and 

 constructed at the laboratory, and is believed to 

 be the first direction-finding coil system ever 

 employed on aircraft, having been used for some 

 experiments at Cranwell in 1916. k complete 

 wireless direction-finding station was shown in 

 operation, the set exhibited being identical with 

 those installed by the Radio Research Board at 

 various universities in the British Isles for experi- 

 mental investigations. 



There were other numerous interesting exhibits 

 in this department, such as the Schuster magneto- 

 meter ; transformers and ovens for experiments 

 on cables at high temperature and high poten- 

 tial ; and methods of measuring the heating 

 of cables buried in the ground under various 

 conditions. 



