410 Scientific Intelligence. 



apparatus is set to as near darkness as possible. The trace of 

 residual light is received upon a rotating mirror, by which it is 

 spread out into a faint band ; on then sending sparks through the 

 coil round the tube of CS 2 the band brightens and presents a 

 distinctly beaded appearance at every spark. Rotating the 

 analyzer a little, every alternate bead grows fainter, while the 

 other alternate ones brighten, thus proving most directly the 

 oscillatory character of the light and of the Leyden jar discharge. 

 —Phil. Mag., April, 1889, pp. 339-349. j. t. 



10. On Limit to Interference ivhen light is radiated from 

 moving Molecules. — In the Annalen der Physik und Chemie, No. 

 2, 1889, Ebert discusses the application of Doppler's principle 

 to the radiation from the moving molecules of an incandescent 

 gas and arrives at the conclusion that the widths of the spectral 

 lines, calculated upon the basis of the principle, are much greater 

 than is consistent with experiments upon interference with a 

 large relative retardation. Lord Rayleigh remarks " that unless 

 this discrepancy can be explained the dynamical theory of gases 

 has received a heavy blow from which it could with difficulty 

 recover. If it be true that a gas consists of molecules in irregular 

 motion, and that for the most part each molecule radiates inde- 

 pendently, there seems no escape from the conclusion that the 

 character of the aggregate radiation must be governed by Dop- 

 pler's principle." Lord Rayleigh therefore examines the subject 

 from a mathematical point' of view, and does not find the dis- 

 crepancy pointed out by Ebert. In the analysis Lord Rayleigh, 

 however, acknowledges that certain assumptions have been made, 

 and regards the question of very great interest and trusts that 

 Ebert will continue his research. — Phil. Mag., April, 1889, pp. 

 298-304. j. t. 



11. Selective Reflection by Metals. — At a meeting of the Phys- 

 ical Society in Berlin, March 8, Dr. Reubens described some 

 experiments upon this subject. The light emitted from an in- 

 candescent plate of zirconium was concentrated by a lens on a 

 mirror surface of the metal under investigation, and the reflected 

 rays were then allowed to fall into a spectroscope with flint glass 

 prism, whose eye-piece had been replaced by a bolometer. The 

 mirror was then replaced by the glowing zirconium, in such a 

 way that the rays of light coming from the point previously 

 occupied by the mirror pursued the same course as in the first 

 experiment. The intensity of light was measured from near F, 

 in the blue, to 2}.i in the red. It was found that silver possesses 

 for blue rays a very considerable reflective power, which reaches 

 its maximum in the red and remains constant for rays of the 

 greatest wave-length. Gold possesses a much smaller reflective 

 power for blue and green rays ; this rises to a maximum in the 

 yellow and falls toward the red. Copper reflects the blue and 

 green rays even less than gold does ; its reflective power increases 

 rapidly into the red, and then somewhat more slowly. In the 

 ultra red it reaches the point of silver. Iron and nickel gg.ve very 



