636 



PHYSICS, PROGRESS OF, IN 1898. 



this area is larger the farther beyond the focus the 

 anti-cathode intersects the cathode stream : (2) that 

 when the intersection is considerably beyond, the 

 area has an intense nucleus surrounded by a halo ; 

 (3) that when the anti-cathode is at 45 to the 

 stream those portions of the stream that impinge 

 most normally produce X rays best ; (4) that at most 

 suitable degrees of exhaustion the cathode stream 

 proceeds almost wholly from a small central portion 

 of the cathode; (5) that the parts of the stream 

 cross at the focus ; (6) that, as S. P. Thompson has 

 pointed out, fluorescence is not due directly to 

 cathode rays, but to what he calls " para-cathodic " 

 rays, proceeding- from the anti-cathode and differ- 

 ing from X rays in power of penetration and in 

 magnetic deflectability. The author suggests that 

 they may consist of rebounding cathode-ray parti- 

 cles that have changed their negative for positive 

 charges, and may thus be identical with anode rays. 

 Morize (Paris Academy of Sciences, Oct. 17) finds 

 by allowing the rays from a Crookes tube to fall 

 through a narrow slit on a rapidly rotating plate 

 that the average duration of total emission of X rays 

 is about one thousandth of a second. Bordier (Paris 

 Academy of Sciences, Feb. 21) finds that the process 

 of osmosis is retarded by exposure to the rays. 

 Wind (Amsterdam Royal Academy, June 25) has 

 found faint evidence of the diffraction of the rays. 

 Trowbridge and Burbank ("American Journal of 

 Science," January) find that fluorspar phosphoresces 

 brightly on heating after exposure to either the 

 X rays or a brush discharge. They think it prob- 

 able, therefore, that the rays produce an electrifica- 

 tion of the fluospar. Villari ("Atti dei Lincei, VII," 

 8) finds that Rontgen rays in traversing a long 

 tube that is opaque to them lose a large part of their 

 power of discharging an electrified conductor. He 

 attributes this to the action of the tube in cutting 

 off lateral rays, which would accelerate the discharge 

 by their effect on the surrounding air. The rays 

 themselves do not seem to be modified by passage 

 through the tube. Sagnac (Paris Academy of 

 Sciences, Feb. 14) finds that air through which 

 X rays pass gives off secondary radiations that affect 

 an electroscope. This action he compares to the 

 shining of a fluorescent liquid. The same investi- 

 gator (ibid., March 21) finds that a metal on which 

 X rays fall emits these secondary rays and that they 

 differ in penetrative power from the original rays. 

 Those from aluminum are more penetrative than 

 those from zinc. The rays produce photographic 

 impressions, excite fluorescence, and discharge elec- 

 trification. They are freely absorbed by aluminum 

 (differing thereby from ROntgen rays), and then 

 give rise to tertiary rays, which are still more read- 

 ily absorbed. De Ileen (Belgian Royal Academy) 

 concludes that every source of disturbance in the 

 ether gives rise not only to known radiations but 

 also to other rays which differ from Rontgen rays 

 only in wave length. They are absorbed so much 

 more readily than ordinary light that our atmos- 

 phere completely sifts them from the solar radia- 

 tion. These rays effect the discharge of conductors 

 and an electric field behaves toward them as an 

 opaque medium. 



Electric Waves. Bose (Calcutta Royal Society; 

 abstract in " Nature,'' Feb. 10) has investigated the 

 refractive index of glass for electric waves to test 

 Maxwell's relation K = jt 2 , in which K is the specific 

 inductive capacity and p. is the refractive index. 

 He found that the refractive index for electric 

 waves was 2.04, while the optical index for the D 

 line is 1.53. Maxwell's relation would therefore 

 make K equal to 4.16. Bose's measurements gave it 

 various values between 2.7 and 9.8. He found the 

 minimum thickness of air space for total reflection 

 between two semi-cylinders with 30 incidence to 



be 13 millimetres; with 60 incidence, between 7.6 

 and 7.2 millimetres. The effective thickness of the 

 air film increases with the wave length. The 

 same investigator (London Royal Society, March 10) 

 finds that the plane of polarization of electrical 

 waves is. rotated by passage along a twisted struc- 

 ture, such as jute fiber. Muriani (" Rendiconti " of 

 the Lombard Royal Academy, XXX, 4) has studied 

 the phenomenon of " multiple resonance " (see "An- 

 nual Cyclopedia," 1890, p. 715) with the aid of the 

 coherer. He finds no evidence of maxima and 

 minima due to nodes and loops, and concludes that 

 the radiations are not simple, but composed of an 

 infinity of waves of different periods. 



Hall Effect. Donau (London Physical Society, 

 June. 24), from a mathematical investigation of the 

 possibility of a Hall effect in a binary electrolyte, 

 concludes that those experimenters who fail to find 

 any such effect are correct. 



High Frequency. Tesla (London Physical So- 

 ciety, Jan. 21) has devised for high-frequency ex- 

 periments an induction coil having in the primary 

 circuit a separate self-inductance coil that is also 

 used as an electro-magnet for the interrupter of 

 that circuit. 



Standard Cells. The determination by Patter- 

 son and Guthe of the electro-chemical equivalent of 

 silver (see " Mechanical Equivalent," under Hear. 

 above) involves a corresponding change in tli 

 electro-motive force of the Clark standard ceL, 

 which would be 1.4327 instead of 1.4342 at 15 C. 



Thermophone. Braun (Wiedemann's " Annalen, ' 

 June) finds that a bolometer, or a strip of brass, put 

 in circuit with accumulators and a microphone 

 may be used to transmit sound by means of the 

 momentary expansions and contractions produced 

 in it by a variable current. 



Telegraphy. Crehore and Squier have devised 

 means for using individual pulsations of a sinusoi- 

 dal alternating current for signaling in high-speed 

 telegraphy. Tests in England show that their 

 synchronograph is capable of transmitting words 

 from three to seven times as fast as the Wheatstone 

 apparatus at present in use. 



Measurements. Blondlot (Paris Academy of Sci- 

 ences, June 13) measures quantity of electricity 

 directly in electro-magnetic units by suspending a 

 ring coil on a vertical axis inside a long horizontal 

 bobbin, the same current flowing through both 

 coils. The product of the current intensity into 

 the time of oscillation is constant, and by adding u 

 device for counting the vibrations a practical cou- 

 lomb meter is made. 



Magnetism. Magnetization. Weyher (Paris 

 Academy of Sciences, Nov. 21) reproduces the prop 

 erties of magnets mechanically by means of com 

 binations of vortices in air or water. The ban; 

 representing the magnets have a wooden axis or 

 which are fastened paper vanes along its whole 

 length. A similar bar set in rotation attracts or 

 repels the first, according as the directions of n>ta 

 tion are the same or opposite ; the neutral zone am 

 other properties of magnets are shown. Mine. 

 Curie (" Bulletin " of the Societc d'Encouragemeni 

 pour I'lndustrie Nationale) finds that steel will 

 1.2 per cent, of carbon is best for permanent ma- 

 nets. Steel does not take temper unless he. 

 above the temperature at which its magnetic proper- 

 ties change. Different metals in steel do not usual!} 

 modify the residual magnetization, but often con 

 siderably increase the field necessary for demagneti- 

 zation (the coercitive field). The greater the coer- 

 citive field the less is the effect of blows. The le>i 

 permanent magnets are made by heating the steel 

 to 60C. and partially demagnetizing it, after hav- 

 ing magnetized it to the saturation point. Kir- 

 stadter (Wiedemann's " Annalen," May), to deter- 



