G44 



PHYSICS, PROGRESS OF, IN 1896. 



lyte, and the unequal velocities due to unequal mo- 

 bility of different ions must be made up by a differ- 

 ence of potential. 



Frictional Electricity. Christiansen (Wiede- 

 mann's ' Annalen." December, 1895) has investigated 

 contact differences of potential between metals by 

 means of so-called "drop electrodes," the terminals 

 of the electrometer being connected respectively 

 with the upper and lower mercury reservoirs, in the 

 latter of which plates of a different metal were im- 

 mersed. He finds that the gas through which the 

 drops fall has considerable influence, platinum be- 

 coming more positive in hydrogen and more nega- 

 tive in oxygen, while other metals are more negative 

 in hydrogen. 



Photo-electricity. Warburg (Berlin Physical So- 

 ciety, May 15) conjectures that gases, unlike elec- 

 trolytes and metals, whose conductivity is independ- 

 ent of strength of current, do not become conduct- 

 ors till the current has reached a certain intensity. 

 Hence the retardation observed in the effect of 

 light in producing the spark discharge may be due 

 to the fact that the gas takes time to become a con- 

 ductor and the action of light may consist in the 

 removal of some obstruction to the establishment 

 of conduction. Elster and Geitel (Wiedemann's 

 " Annalen," January and March) find that the ap- 

 parent dissipation of charge when an anode is il- 

 luminated in a vacuum is due to the effect of the 

 light on the platinum cathode or on the interior of 

 the tube when it has acquired a slight coating of 

 alkali-metal vapor. They also find that the brushes 

 and sparks from a Holtz machine passing between 

 a cathode plate of zinc and an anode sphere of any 

 metal are replaced by a glow discharge when short- 

 wave light illuminates the cathode. The quantity 

 of electricity that passes is also smaller. Lodge 

 (" Science Progress," August) has experimented to 

 test the presence of metallic particles or vapor near 

 an electrified metal that is rapidly discharging un- 

 der the action of light. He concludes that the 

 discharge of electricity from illuminated surfaces 

 is not effected by evaporation of those surfaces, but 

 that the molecules which convey the charge belong 

 to something in the gas and not to the illuminated 

 body. The conviction deepens everywhere that 

 photo-electric phenomena are due to convection, but 

 . its mechanism remains undiscovered. 



Low-pressure Phenomena in Oases. Gossart and 

 Chevalier (Paris Academy of Sciences, Feb. 10) de- 

 scribe a new mechanical action proceeding from a 

 Crookes tube. In attempting to show the heating 

 effect of such a tube by means of a radiometer they 

 found that the latter did not rotate, but took up a 

 fixed position under control of the tube. If the 

 radiometer arms were set in motion, there were os- 

 cillations about this position, more rapid the nearer 

 the radiometer was to the tube. Nipher (St. Louis 

 Academy of Science, May 4) has observed a rota- 

 tional movement of the cathode disk in a Crookes 

 tube. The motion was not affected by magnets and 

 appears to be due to reaction between the disk and 

 the radiant matter. If so, the latter must start 

 from the disk in a vortex whose axis passes through 

 the dark spots opposite to it. Paalzou and Neesen 

 (Wiedemann's " Annalen," December, 1895) find that 

 the medium in which discharge tubes are immersed 

 has a decided influence on them, water and alcohol 

 extinguishing the glow. The effect is not due to 

 condensation, for the total current was lessened and 

 the 'effect required time. Any motion of electricity 

 near by, such as electrification or discharge of the 

 outer surface of the tube, or the approach of a 

 charged body, favored the internal discharge. El- 

 ster and Geitel (Wiedemann's " Annalen," Decem- 

 ber, 1895) find that electric oscillations may cause 

 peculiar movable light phenomena in rarefied gases. 



In a discharge tube that is surrounded by a con- 

 ducting ring in connection with the earth, and that 

 touches another conductor connected with a strong 

 induction coil, a pencil of bluish light is formed at 

 a vacuum of O'Ol to O001 millimetres of mercury. 

 The approach of a conductor or a magnet causes 

 this light to assume various shapes and positions. 

 Wood (Wiedemann's "Annalen," October) has meas- 

 ured temperatures within a vacuum tube by using 

 a platinum spiral as a bolometer. At an internal 

 pressure of 3 millimetres the rise of temperature 

 varied from 13 to 25'7 C. as the current varied 

 from 0-0015 to 0-0036 ampere. The bright spaces 

 were always a few degrees hotter than the dark ones. 

 In a later article (" Physical Review," November- 

 December) the author states that in no case does 

 the temperature within the tube exceed that of the 

 outer air by more than 20 or 30 degrees, and that it 

 varies definitely from point to point. In passing 

 from a bright to a dark stratum there is sometimes 

 a change of 5. Pupin (" Electrical Age," March 

 28-April 25) has made special experiments on the 

 behavior of electrical discharges through poor vacua, 

 when such discharges are produced by means of the 

 condenser effect of tin-foil coatings or other con- 

 ductors placed on the outside of a vacuum jar. 

 When one electrode is such a coating on a glass 

 bulb, and the other is a brass sphere, the discharges 

 bear striking resemblance to the phenomena of the 

 solar corona. Moore (American Institute of Elec- 

 trical Engineers, April 22) has achieved noteworthy 

 results in vacuum-tube lighting by means of an in- 

 vention that he calls a " vacuum vibrator," which 

 is practically the interruptor of an induction coil 

 working in a vacuum, the actuating magnet being 

 without. The breaks can thus be made very sud- 

 denly without danger of sparking, and the resulting 

 intensity of illumination is great. 



Cathode Rays. Jaumann (Wiedemann's " An- 

 nalen," October) finds that cathode rays may be 

 temporarily deflected by moving electrified bodies, 

 the effect differing totally from the permanent de- 

 flection due to neighboring conductors. De Heen 

 (" Bulletin de 1'Academie Royale de Belgique ") 

 advances the theory that cathodic and anticathodic 

 rays result from encounters between molecules pro- 

 jected from the cathode and anode respectively. 

 When adjacent parallel laminae are used as anode 

 and cathode no anticathodic rays are observed, 

 whereas, according to the ordinary theory, there 

 should be great numbers of them. De Heen sup- 

 poses, on his theory, that the intervening space is 

 too small to allow of" frequent collisions. (For other 

 phenomena, see RONTGEN RAYS.) 



Electric Waves and Radiation : Detection and 

 Measurement. Rutherford (British Association) de- 

 tects electro-magnetic waves by a group of fine steel 

 wires, insulated from each other by shellac, which 

 are first magnetized and are then inserted in a coil 

 that is provided with a suspended magnet and mir- 

 ror. The passage of the waves alters the magnet- 

 ism of the group and moves the mirror. The de- 

 tector will respond to long waves at a distance of 

 half a mile ; for short ones it is less sensitive. Lang 

 (Wiedemann's " Annalen," March) has measured the 

 wave length of electric waves by a method similar 

 to that of Quincke for measuring the wave length 

 of a musical tone. Quincke's method depends on 

 the arrangement of the lengths of two tubes which, 

 starting from near the source of sound, are brought 

 together at their other end, so that the sound that 

 has traveled through one tube interferes with that 

 through the other. The tubes in the electric meas- 

 urement are of paper lined with tin foil. 



Electric Waves : Absorption. Planck (Wiede- 

 mann's " Annalen, January) divides the absorption 

 of electric waves by resonance into three stages: 



