6o 



NA TURE 



[May 2 1, 1908 



new object-glass for high-power magnification. The 

 objective exhibited, used with an ordinary eye-piece, 

 constitutes a high-power ocular capable, in combination 

 with an ordinary high-power objective glass, of yield- 

 ing a perfect image up to magnifications of eight or 

 ten thousand diameters. Being self-contained, that is to 

 say, independent of external influences, it can be used in 

 any position, and is therefore as well adapted to use with 

 the telescope as with the microscope. 



Mr. ], E. Barnard : Mercurv vapour lamps for micro- 

 scopic illumination. Mercury vapour lamps have consider- 

 able advantages as illuminants for microscopic work, as 

 their visible spectrum consists chiefly of three bright lines, 

 one each in the orange, green, and ijlue-violet. It is there- 

 fore possible, by using suitable absorbent colour screens, to 

 transmit only one bright line of the required colour, the 

 remaining ones being absorbed. The source of light then 

 becomes truly monochromatic, and is practically of one 

 wave-length. — Mr. Conrad Beck: (1) Diffraction patterns 

 (antipoints) of point source of light viewed under the micro- 

 scope with apertures of different shapes illustrating the 

 influence of the aperture shape on microscopic resolution ; 

 (2) living bacteria, shown on a dark ground with 1/12 oil 

 immersion lens visible by their own reflected light. 



Prof. T. Turner : Transparent films of silver and other 

 metals. Gold leaf supported on a glass plate and heated 

 to about 550° C. loses its green colour and transmits white 

 light. Silver leaf heated in air or oxygen to 400° C. be- 

 comes remarkably transparent, transmitting white light. 

 The action begins at about 250° C. Copfer leaf remains 

 opaque if heated in a reducing atmosphere to 500° C. 

 When heated in air for about an hour to 250°, or for a 

 much shorter time to higher temper:itures, the copper be- 

 comes transparent and transmits a brilliant green light. 

 This colour continuously darkens with further heating. 

 .'\luminium leaf does not become transparent either in an 

 oxidising or reducing atmosphere. Dutch metal skeleton- 

 ises, but remains opaque. — Mr. S. D. Chalmers: Models 

 illustrating refraction at plane and spherical surfaces. 

 These models illustrate the influence of reduced velocity in 

 glass on the form or direction of waves. The curvatures 

 of the incident and refracted waves are indicated by flexible 

 rods ; the paths from a point on the incident to the corre- 

 sponding point on the refracted wave are indicated by cords 

 of constant length. 



Dr. W. J. Russell, F.R.S.: Pictures showing the action 

 of various coals on photographic plates in the dark. These 

 pictures of different coals were obtained bv cutting vertical 

 sections of the coal and laying them on a photographic 

 plate in the dark, at a temperature of about 50° C, for 

 seven to twenty-four -hours. The photographic plate was 

 then developed, and the picture printed in the ordinary 

 way. — Prof. J. Symington, F.R.S., and Dr. J. C. Rankin : 

 .\ series of skiagrams illustrating the development of teeth 

 in man. The skiagrams were taken from one lateral half 

 of a series of skulls aged from birth up to pubertv. 



Mr. S. Cowper-Coles : (i) Specimens of bimetallic para- 

 bolic mirrors made by electro-deposition. The parabolic 

 mirrors are composed of bands of yellow and white 

 metal, and are made by a combined process of electro- 

 deposition and spinning. (2) Specimens of pure electro- 

 lytic iron. Pure electrolytic iron sheets made direct in 

 one operation by a process of electro-deposition from 

 pig iron or ore without any rolling, with a tensile 

 strength of about thirty tons to the inch ; the iron is 

 free from crystalline structure. — Mr. F. W. Aston : 

 New dark space in helium. The tube exhibited contained 

 helium at a pressure of about 3 mm. It was provided with 

 aluminium electrodes, the kathode being a large flat plate. 

 .\ continuous current of low densitv was passed through. 

 Under these conditions the " Crookes dark space " is ill- 

 defined and filled with a greenish glow, while next to the 

 kathode is seen a narrow region of intense darkness .sharply 

 defined. The fall of potential across this " new dark 

 soace " appears to be invariably about 30 volts. — Dr. /. .4. 

 Fleming, F.R.S. : (_i) Apparatus for exhlbitine photo- 

 electric effects with potassium-sodium alloy. The alloy 

 was enclosed with an insulated platinum plate in an 

 exhausted tube. When the olate and alloy were con- 

 nected to a galvanometer and the surface of the allov 

 illuminated hy an arc lamp, an E.M.F. of about oS volt 



NO. 2012, VOL. 78] 



was created, and a current produced in the circuit by 

 the light. (2) Oscillation valves or glow-lamp electric- 

 wave detectors used for receivers in long-distance wire- 

 less telegraphy. It was shown by the exhibitor in 

 1904 that a carbon filament glow-lamp, having in its 

 bulb a metal cylinder surrounding the filament carried 

 on an insulated terminal, could be used in combination 

 with a galvanometer or telephone as a wave detector in 

 wireless telegraphy, owing to the emission of negative 

 electricity from the incandescent carbon. Such a device 

 was named by him oscillation valve, and is a verv sensitive 

 long-distance receiver. Glow-lamp detectors of the type 

 exhibited have been used as receivers in Transatlantic wire- 

 less telegraphy, and are also of use as receivers for wire- 

 less or radiotelephony. (3) A recent form of cymometer 

 or instrument for measuring the length of the waves 

 radiated by, and the damping of the oscillations in radio- 

 telegraphic antenna?. — .Mr. I.. H. Walter: (i) Tantalum 

 wave-detector for wireless telephony or telegraphy. A 

 tantalum wire point dipping into mercury is spontaneously 

 restoring. At 450 miles, using less than 2 kilowatts, the 

 results equal those of the electrolytic detector. The sound 

 is louder than with the electrolytic when the signals are 

 not too weak. (2) New electrolytic signalling key. A 

 water-cooled signalling key for higher powers [2 kilowatts 

 upwards). A local key circuit actuates two valve elec- 

 trodes, normally separated, and having the whole primary 

 voltage across them, so that the cell is short-circuited 

 beneath the electrolyte. {3) Model of an experimental form 

 of the exhibitor's magnetic detector of 1906. 



The National Physical Laboratory. Mr. A. Campbell : 

 (i) Moving-coil vibration galvanometer. This instrument 

 belongs to the class of tuned galvanometers first intro- 

 duced by Prof. M. ^\'ien. Its novelty consists in the use 

 of the moving-coil system. (2) Variable mutual inductance 

 standard. Designed for the measurement of small induct- 

 ances and capacities. (3) Standard of mutual inductance 

 calculable from the dimensions. A small model of the 

 large mutual inductance (10 millihenries) recently com- 

 pleted at the National Physical Laboratory. (4) Secondary 

 standard of mutual inductance (subdivided). Mr. W. 

 Rose)tliain : (5) Ouenching apparatus for metallographic 

 specimens, for quenching small specimens of metal in vacuo 

 without removing them from the furnace. Mr. W. Rosen- 

 hain, Mr. F. C. A. H. Lantsberry, and Mr. P. A. Tucker: 

 (6) Composite photoinicrographs representing relatively 

 large areas of steel. Mr. W. Rosenhain : (7) Tensile frac- 

 ture of steel under the Zeiss stereoscopic microscope. — Rev. 

 F. J. Jervis-Smith, F.R.S. : Apparatus for generating a 

 luminous glow in an exhausted vessel, moving in an 

 electrostatic field, and exhibiting the action of a rriagnetic 

 field on the glow so produced (see p. 70). — Mr. J. T. 

 Irwin : Hot wire oscillograph. — Mr. S. G. Brown : Experi- 

 ments with a high-frequency alternator. 



Mr. R. Threlfall, F.R.S. : Laboratory apparatus for ex- 

 periments under verv high measured pressures and at very 

 high temperatures — pressures up to 100 tons per square 

 inch, temperatures up to 2000° C. Advantage is taken of 

 the practically perfect fluidity of crystalline graphite at 

 high pressures, and of the solidity of compressed magnesia, 

 zirconia, &-c., to construct an apparatus on the laboratory 

 scale for such experiments as the possible transformations 

 of carbon under high temperatures and pressures. — Prof. 

 T. B. Wood : The factors which influence the baking value 

 of wheat flour. The " strength " or baking value of wheat 

 is determined by two main factors : — (i) high diastatic 

 capacity, which continuously produces sugar in the dough, 

 and thereby enables the yeast to keep up a continuous 

 evolution of carbon dioxide ; (2) suitable concentration of 

 acid and salts in the flour, which affects the physical 

 properties of the gluten, and hence the shape of the loaf. 

 — Dr. T. E. Thorpe, F.R.S. : (i) Apparatus and specimens 

 used in connection with the determination of the atomic 

 weight of radium ; (2) glass and Quartz vessels coloured 

 under the influence of radium. — Sir William Crookes. 

 F.R.S.: Scandium, its salts, and its position in the scheme 

 of the chemical elements. Scandium is an exceedingly 

 rare terrestrial element, occurring in very few minerals 

 and in verv small amount — usually not more than o-oi per 

 cent. The one exception is the rare mineral wiikite, which 

 contains scandium in considerable quantity. Astronomical 



