318 Scientific Intelligence, 



p. 622, 1894) and illustrates its accuracy in comparison with pre- 

 vious electrometer methods and with the glass trough method. 

 Under his direction J. F. Smalk has employed two electrometers 

 of the form designed by Bjerknes, in which a needle is acted on 

 inductively by two quadrants, which are connected to the ter- 

 minals of a Ruhmkorf coil. The needle and the quadrant are 

 immersed in the dielectrics which are to be compared. It is 

 pointed out that the needle of the electrometer must be placed in 

 a comparatively large mass of the dielectric, which must also fully 

 surround the electrodes or quadrants. J. F. Smale describes an 

 ingenious gas regulator to obtain uniform revolution of the arma- 

 ture of a little alternating machine which excited the transformer 

 which was connected with the electrometers, which in turn were 

 connected in parallel. Smale found a satisfactory agreement 

 between the electrometric method and the bridge method 

 employed by Nernst. — Ann. der Physik und Chemie No. 2, 1896, 

 pp. 209-222. j. t. 



10. Dielectric Resistance. — P. Drude elaborates the conception 

 of dielectric resistance to lines of electrostatic force, analogous 

 to the conception of magnetic resistance previously touched upon 

 in his treatise " Physik des Aethers "; and also by Professor Nipher, 

 of Washington University, St. Louis. — Ann. der Physik und 

 Chemie No. 2, 1896, pp. 223-231. j. t. 



11. Index of refraction and reflective power of water and alco- 

 hol for Electric Waves. — If the wave length of electric waves 

 along two parallel wires is measured, first with air between such 

 wires and afterwards when a portion of the space between them 

 is filled with a dielectric, the ratio of the resulting wave lengths 

 will give %he index of refraction of the dielectric for the electric 

 waves. A. D. Cole, working in this manner, has obtained 8*95 

 for the index of refraction of water at 19° C. and 5*2 for alcohol 

 at 18° C. With the employment of mirrors to reflect the electric 

 waves from the surfaces of water and alcohol, it was found that 

 waves 5 cm long gave with reference to Fresnel's formula, both 

 for rays polarized perpendicular to the plane of incidence and 

 also parallel to it, the same value for the index of refraction (cal- 

 culated from observed reflective power). For water n=zS-8 and 

 for alcohol n=3-2. With alcohol the index of refraction was 

 much greater for long electric waves than for short. — Ann. der 

 Physik und Chemie No. 2, 1896, pp. 290-310. j. t. 



12. Pontgen Pays. — Righi, in a preliminary paper (Rendiconto 

 delle Sessioni della R. Accademia delle Scienze di Bologna, Feb. 

 9, 1896), states that the Rontgen rays have the property of dis- 

 pelling positive charges of electricity as well as negative. Pro- 

 lessor J. J. Thomson has independently made the same observa- 

 tion. (Nature, Feb. 27, 1896.) Professor Thomson also states 

 that when the Rontgen rays pass through any substance they 

 make it for the time a conductor of electricity. This explains the 

 fact that an electrified plate in air loses its charges whether it be 

 electrified positively or negatively. The air is converted into a 



