PHYSICS, PROGRESS OF, IN 1898. 



633 



powerfully photo-electric. Guillaume (" Revue Ge- 

 lu'nile des Sciences," Dec. 15, 1897), discussing an 



experiment of Burke that seems to show that fluo- 

 rescent bodies are more strongly absorbent while 

 fluorescing, suggests that the molecules are excited 

 momentarily to a forced vibration and become for 

 an instant susceptible of absorbing vibrations of 

 the same period. He would bring the phenomenon 

 under Kirchhoff's law by suppressing altogether the 

 idea of temperature in this law. Villard (Paris 

 Academy of Sciences, May 16) finds that those parts 

 of a fluorescent screen that have been in shadow are 

 more luminous when the object is removed than 

 the parts previously illuminated. Wesendonck 

 (Wiedemann's " Annalen," December, 1897) finds 

 that a luminescent body is capable of imparting 

 heat to a body warmer than itself, but that there is 

 no contradiction of the second law of thermody- 

 namics, as there is no ordinary thermal radiation. 

 Burke (British Association) has made the luminos- 

 ity produced by striking sugar practically contin- 

 uous by using a hammer to strike the rim of a re- 

 volving disk of sugar about twice a second. The 

 luminosity extends from the hammer inward and 

 downward, and its spectrum is confined to the more 

 refrangible side of the F line. The nature and ap- 

 pearance of the light are not dependent on the 

 surrounding medium. 



Becquerel Rays. Stewart (" Physical Review," 

 April) in a general review of the subject concludes 

 that Becquerel rays are due to transverse ether 

 waves, but that owing to feebleness and short wave 

 length it is doubtful whether their interference can 

 ever be shown. They are non-homogeneous, like X 

 rays, and their similarity in behavior to these is a 

 strong argument in favor of the short-transverse- 

 wave theory of X rays. Schmidt (Wiedemann's 

 " Annalen," May) finds that thorium compounds and 

 some other substances give out Becquerel rays dif- 

 fering from those that proceed from uranium in not 

 being polarized by tourmaline and in being less 

 powerful, as measured by the time required to dis- 

 charge an electrified plate. Russell believes that this 

 ray-emitting power may be a general property of 

 matter, for nearly every substance affects a sensi- 

 tive plate in darkness, if given time enough. He 

 shows in the Bakerian lecture before the London 

 Royal Society, March 24, that certain metals and 

 organic substances can produce images on a photo- 

 graphic plate, the activity of the organic substances 

 being the greater. Printer's ink and copal varnish 

 both are of this class, owing to the linseed oil in the 

 former and the turpentine in the latter. Vegetable 

 oils and essential oils containing terpenes are all 

 active. All substances having similar effects are 

 reducers, absorbing oxygen, and this apparently 

 causes their power. The action, however, can take 

 place through thin layers of certain solid bodies for 

 instance, gelatin, celluloid, and gutta-percha; but 

 others, such as glass and mica, prevent all action. 

 Elevation of temperature increases the action. Of 

 common metals, zinc gives the best results. The 

 active metals are, in order, magnesium, cadmium, 

 zinc, nickel, aluminum, lead, and bismuth. The 

 metallic surface must be brilliant. Inactive liquids, 

 such as alcohol, if soaked in an active metal for a 

 few days, become active. Further experiment in- 

 dicates' that the phenomenon is due to an actual 

 emanation and not to luminescence. M. and Mine. 

 Curie (Paris Academy of Sciences, July 18) have 

 shown that the activity of pitchblende as a source 

 of Becquerel rays is due to a new substance, which 

 they have named polonium. 



Electro-magnetic Theory. Buisson (Paris Acad- 

 emy of Sciences, Feb. 7), to test the relation be- 

 tween transparency and electrical resistance re- 

 quired by the electro-magnetic theory of light, has 



measured the transparency of a thin sheet of bi>- 

 muth whose resistance was caused to vary suddenly 

 by placing it in an electro-magnetic field* No vari- 

 ations in the transmitted light being observed, the 

 author concludes that the conductivity that affects 

 transparency is of a different order from the usual 

 kind. 



Pseudoscope. Solomons (" Nature," Feb. 3) has 

 devised a pseudoscope with which an approximate 

 stereoscopic effect can be obtained with a single 

 picture. A large, deep cylindrical lens is cut into 

 two wedges, each having one flat and one curv.-d 

 side. These are placed together with the thick por- 

 tions toward each other and held at a short dis- 

 tance over the picture. Two images result, each of 

 which is compressed on the inner side, which is a 

 property of the ordinary pair of stereoscopic views. 

 By viewing these images with stereoscopic lenses the 

 impression of solidity is produced, unless the original 

 picture contained an object very near the observer. 



Electricity. Resistance. lie Chatelier (Paris 

 Academy of Sciences, June 20) finds that tempering 

 does not modify the resistance of steel except when 

 it takes place above the temperature of recalescence 

 (710). The resistance then increases with the tem- 

 perature of tempering, up to a value higher as the 

 steel is richer in carbon. The increase of resist- 

 ance in iron due to the presence of carbon aver- 

 ages 45 microhms for an addition of 1 per cent, by 

 weight of carbon. The same is true of silicon. Le 

 Roy (ibid., Jan. 17) has measured the resistance of 

 crystallized silicon, which he finds to be 1,300 times 

 that of electric-light carbon. It diminishes on 

 heating, falling 40 per cent, for a rise of 800 C. 

 Gressman (American Association) reports that lead 

 amalgams show a remarkable sudden decrease in 

 resistance upon solidification, the resistance of the 

 solid amalgam being sometimes as low as one fifth 

 of the resistance of the fluid amalgam at its freezing 

 point. If the thermoelectrical explanation based 

 on heterogeneity of excessively high resistance of 

 alloys is correct, an increase of resistance upon 

 solidification would seem probable, for it is then 

 that the alloy becomes heterogeneous. Branly 

 (Paris Academy of Sciences, July 25) finds that 

 although two smooth plane disks of zinc or copper 

 when pressed together offer practically no resistance 

 to the current, disks of iron, aluminum, or bismuth 

 give a small resistance, which is greatly increased 

 when they are brought forcibly together by falling 

 from a he'ight. M. Branly is unable to explain this 

 fact. In 1877 Bosi ("Il'Nuovo Cimento," April) 

 described experiments that seemed to show that a 

 very moderate velocity (10 or 12 centimetres a 

 second) of an electrolyte with or against a current 

 flowing through it changed its resistance. Hay ward 

 (" Physical Review," November) has been unable to 

 detect any such action, using a 5-per-cent. solution 

 of copper sulphate with a velocity of flow of 8 

 to 11 centimetres a second. Haagn (; Zeitschrift 

 fiir physikalische Chemie "), in an investigation of 

 the internal resistance of galvanic couples, comes 

 to the following conclusions: 1. The internal 

 resistance of galvanic elements with simultaneous 

 electrolysis is independent of current intensity, the 

 slight oscillations being due to changes of concen- 

 tration. 2. In accumulators a slow increase of re- 

 sistance takes place at first, and this becomes more 

 and more rapid during the discharge, while during 

 the charging the changes of resistance are in in 

 order; these arise from the deconcentration of the 

 sulphuric acid and the production of a pa- 

 resistance at the electrodes, especially at the per- 

 oxidized one. Fawcett (British Association) has 

 constructed standard high resistances of great con- 

 stancy bv depositing cathode films on glass and 

 heating them for a long time in a partial vacuum. 



