252 Scientific Intelligence. 



filled with air, which dilates under the influence of radiation, 

 forces back the zinc sulphate solution in the tube, and thus greatly 

 increases the electrical resistance on that side. The apparatus is 

 made symmetrical to eliminate variations of pressure and tem- 

 perature. This radiometer will indicate one hundred millionth of 

 a degree. The moon's radiation gives a galvanometer deflection 

 of five divisions. — Nature, p. 157, Dec. 15, 1887. j. t. 



9. Velocity of Sound. — At a meeting of the Physical Society, 

 London, Nov. 12, Prof. A. W. Rucker exhibited an apparatus 

 for determining the velocity of sound on the principle employed 

 by Fizeau for measuring the velocity of light. " A vibrating 

 reed is used as the source of sound and a sensitive flame as the 

 receiver. A long U-sliaped tube has its two ends placed near 

 and parallel to the plane of a perforated disc, which is capable of 

 rotating about an axis perpendicular to its own plane. The reed 

 and sensitive flame occupy similar positions on the opposite side 

 of the disc. On rotating the disc the sensitive flame flares or is 

 quiescent according as the time taken to travel the length of the 



T 



tube is an even or an odd multiple of — , where T is the time of 



one revolution and n the number of holes in the disc." — Nature, 

 p. 119, Dec. 1, 1887. J. t. 



10. On the transmission of power by alternating, electrical cur- 

 rents. — Mr. T. H. Blakesley, in a communication to the Physical 

 Society, London, Nov. 12, discussed the relative efficiency of the 

 transmission of power by direct and by alternating dynamos, and 

 concludes that the ratio of power to weight is much greater for a 

 direct than an alternating current motor. The author considers 

 this a great drawback to the employment of the latter. He also 

 showed that by placing a condenser between the terminals of the 

 recipient machine a greater current could be passed through the 

 receiver than that in the generator and line. — Nature, p. 119, 

 Dec. 1, 1887. J. t. 



11. Measurement of Electromotive Forces. — Sir William Thom- 

 son has employed his new deciampere balance to the determina- 

 tion of the electromotive force of a Clark cell. The result ob- 

 tained was 1-436 volts at 15° C. The result obtained by Lord 

 Rayleigh was 1-435 at ±5° C.—Phil. Mag., p. 514, Dec, 1887. 



J. T. 



1 2. Influence of Magnetism on the TJier mo-electric behavior of 

 Bismuth. — Dr. Giovanni Pietro Grimaldi shows that the ther- 

 mo-electric behavior of bismuth in 'relation to copper is weakened 

 by magnetism. The diminution of the electromotive force was 

 about -gL — , and seemed to be of the same order of magnitude as 

 the variations in electrical resistance investigated by Righi. — 

 Mendiconti della R. Accademia dei lincei, Feb., 1887. J. t. 



13. Coincidences between lines of different Spectra. — The diffi- 

 culty of deciding upon the existence of a metal, like cerium, in the 

 sun, is very great, since, on account of the number of lines in the 

 spectrum of the metal, the probability of many of its lines coin- 

 ciding in position with lines in the solar spectrum is very great. 



