618 SCIENTIFIC RECORD FOR 1883. 



sistance to the passage of electricity, maintaining that the resistance 

 experienced is due to a counter electromotive force, increasing with the 

 rarefaction and connected with the electrodes, In exhausted tubes, 

 without electrodes, simple friction produces an electrical glow. (Phil. 

 Mag., January, 1883, V, xv, 1.) 



Naccari has examined the heating produced in the electrodes by the 

 induction spark. (J. Phys., II, II, 521.) Hertz has communicated to the 

 Berlin Physical Society some curious results observed by him in the 

 case of electric discharges in air and other gases under a pressure of 

 from 20 to 30 mm of mercury. (Nature, xxvn, 403.) Goldstein has stud- 

 ied the electric discharge in rarefied gases, especially the so-called re- 

 flection of electric rays. (J. Phys., II, II, 179.) Worthington has suc- 

 ceeded in showing that the phenomena of induction take place across 

 a discharge-resisting vacuum. Hence this vacuum cannot be a con- 

 ductor, at least in the ordinary sense. (Nature, March, 1883, xxvn, 

 434.) De la Eue and Miiller have communicated to the Royal Society a 

 paper on the electric discharge produced with the chloride of silver 

 battery of 11,000 cells. (Nature, August, 1883, xxvm, 381.) 



Dewar has made a series of manometric observations upon the elec- 

 tric arc. The two carbons used were hollow, and had an interior diam- 

 eter of 3 mm . Their porosity had been destroyed by heating them to 

 a white heat in a porcelain tube, through which benzene vapor was 

 passed, thus depositing compact carbon on their surfaces. The car- 

 bons were connected to the interior of two closed flasks, at the bot- 

 tom of which was ether or other mobile liquid, into which also passed 

 the recurved end of a long horizontal tube serving as a manometer, 

 and showing a variation of 0.004 mm pressure. When the arc is well 

 formed, being sharply limited by an almost spherical surface, envelop- 

 ing the extremity of the positive carbon and just touching the end of 

 the negative, an increase of pressure of one to two millimeters of water 

 is seen at the positive electrode, and a slight decrease at the negative. 

 When the arc hisses, the positive pressure diminishes. When the 

 negative pole throws off incandescent particles, the pressure increases. 

 (Proc. Roy. Soc, xxxin, 262; J. Phys., January, 1883, II, n, 42.) 



Siemens and Huntington have described the modified form of electric 

 furnace lately employed by them. Its novelty consists in the fact that 

 the negative electrode, which passes through the cover of the crucible, 

 is suspended to one end of a lever, to the other end of which is a hol- 

 low cylinder of iron moving within a coil, and adjustable by a counter- 

 weight. Since the coil, which is placed in shunt circuit, has a high 

 resistance, its attractive force on the cylinder is proportional to the 

 electromotive force between the carbon points, i. e., to the resistance of 

 the arc, the length of which is thus automatically regulated. The ad- 

 vantages of this furnace are, 1st, the temperature is limited only by 

 the refractory resistance of the crucible; and, 2d, the heat is applied 



