Si Scientific Intelligence. 



10. Use of the Thread Galvanometer. — W. Einthoven de- 

 scribed in Ann. der Phys., p. 1059, 1903, a galvanometer which 

 consisted in the main of a silvered quartz fiber stretched between 

 the poles of a magnet. He now explains some further peculiar- 

 ities and uses of the instrument. He has repeated the Curies' 

 measurement of radio-activity of various substances by the use 

 of his instrument instead of the electrometer and finds it more 

 suitable for the purpose. The currents measured were of the 

 order 5 X ] -11 amp. He also measured insulation resistances of 

 the order of a million megohms. A quantity of electricity 

 5X10~ 12 ampere-seconds can be detected. In general the instru- 

 ment is suitable for many uses to which the electrometer has 

 been put ; and it is especially useful to detect and measure feeble 

 sounds or telephone currents. — Ann. der Phys., No. 6, pp. 182-1 92, 

 1904. j. t. 



11. The Hot Oxide Coherer. — Max Hoenemann states that he 

 described this coherer in 1902, while Branly's paper on the same 

 subject appeared in 1904. Heated and then cooled particles of 

 iron possess, on account of the layer of oxide, a peculiar sensitive- 

 ness to electrical waves. The author had shown this property of 

 cold oxide layers and lately has investigated the influence of 

 heat on the sensitiveness of such layers. He found that hot 

 layers of the oxide, if they are of the same metal throughout, do 

 not possess any marked superiority over the cold particles ; but 

 if he used layers of different metals, for instance, lead with an 

 oxidized (not noble) metal,- he obtained a much greater sensitive- 

 ness. With a hot lead copper contact he could detect the purring 

 of a little induction coil at a distance of 12 meters and through 

 intervening walls. 



Hornemann has studied this effect of the heated oxide layer 

 by means of a galvanometer and suitable electric circuits ; but is 

 not certain of the reason for this peculiar action of heat on the 

 coherer. The property seems to be an important one with refer- 

 ence to wireless telegraphy. — Ann der Phys., No. 6, pp. 129— 

 138, 1904. j. t. 



12. X-Bays and X-Bays ; by R. Blondlot. — * * * * The 

 consideration of the kind of symmetry belonging to a Crookes' 

 tube suggested to me the possibility that the rays emitted by it 

 might be polarized on their emission. I proved, in fact, that a 

 small electric spark, subjected to their action, increased in bril- 

 liancy when the discharge was parallel to the axis of a Crookes' 

 tube, and that this reinforcement did not take place when normal 

 to the axis. This indicated that the rays emitted had indeed the 

 want of symmetry characteristic of polarization. This point 

 established, I demonstrated at once the existence of rotatory 

 polarization : quartz, sugar, etc., served to rotate the plane of 

 polarization of the radiations produced by a Crookes' tube. I 

 then conceived the idea of trying the rotation by a series of mica 

 plates, after the manner of Reusch : this rotation in fact took 

 place. I was thus led to examine the effect of a single lamina 



