Chemistry and Physios. , 227 



partly at least by direct electric action on the sensitive film which 

 would be usually understood as a purely photo-chemical cause. — 

 Phil. Mag., Dec, 1888, p. 502. j. t. 



13. Spectrum of Cyanogen and Carbon. — H. W. Vogel has 

 -examined the spectra of the Bunsen flame, the cyanogen flame, 

 the electric light and the various oxides of carbon with the elec- 



1 trie spark, and has photographed with Azalin plates the spectra 

 from the orange to the ultra violet. The spectra were photo- 

 graphed over each other in order to measure coincidences. After 

 a discussion of the various bands and lines observed in the differ- 

 ent sources of light, the author concludes that the cyanogen 

 spectrum is identical with that of carbon. It seems to him that 

 carbon can emit two spectra — one which gives the bands to the 

 Bunsen flame and another the group of lines which appear clearly 

 in the spectrum of cyanogen when seen by the aid of the electric 

 arc. The channelled bands of the cyanogen spectrum in the red 

 and yellow can be attributed to a compound. A full and re- 

 markable coincidence of an especially bright indigo colored band 

 with the dark back-ground of the G band of the solar spectrum 

 appears in all the spectra. Vogel therefore attributes the dark 

 back-ground of the G line to carbon in the sun. — Sitzungsber. d. 

 Berliner Ah., 21, 1888. ' j. t. 



14. Determination of the focal length of a lens for different 

 colors. — Hasselberg places the objective upon a suitable bar 

 somewhat more than four times the focal length of the lens and 

 obtains, in two positions, clear images of the spectral lines formed 

 by aid of a collimator and suitable prisms. If E is the length of 

 the bar, e the difference of both positions of the objective, one 

 has 4/^E— £ 2 /E in which the thickness of the lens is neglected. 

 — Bull, de VAc. des 8c. de St. Pet., xxxi>, p. 412, 1888. j. t. 



15. Electrodynamic Waves. — At a late meeting of the Physical 

 Society of Berlin, Helmholtz gave an account of the recent 

 researches of Hertz on the propagation of electrical waves. 

 Weak induction discharges between small metallic cylinders with 

 rounded ends were employed, and a similar apparatus for the 

 detection of the electrodynamic waves. The action was not 

 propagated more than 2 or 3 meters through space ; when it fell 

 on a metallic surface it was reflected, interference phenomena 

 were observed and from these the length of half a wave was 

 found to be 30 centimeters. When a metallic parabolic mirror, 

 1 meter across its opening, was placed behind the apparatus used 

 to produce the discharge, the action was propagated to a dis- 

 tance of 8 meters ; and the action was greatly increased when a 

 second concave mirror was placed behind the receiving apparatus. 

 When a conductor was interposed the action ceased, while non- 

 conductors allowed the waves to pass. By interposing perforated 

 metallic screens, it was found that the waves are propagated in 

 straight lines; the waves passed through a dry wooden pai'tition. 

 Polarization of the waves could be determined in several ways. 

 When the receiver was placed at right angles to the apparatus 



