PHYSICS, PROGRESS OP, IN 1900. 



573 



exceed 5 amp&res, and probably a faintly luminous exceed 0.01 micro-second, the spark probably does 



.lobe as large as one's head might be formed 

 with a current as weak as 0.01 ampere. Leduc 

 (Eclair Electrique, Oct. 28, 1899) reports that fine 

 polished metallic points from 5 to 10 centimetres 



not last more than 0.4 micro-second. 



Electric Arc. Child (Physical Review, March) 

 discusses Brown's discovery, made by photography, 

 that the arc is formed by the coalescence of two 



apart, at right angles to a photographic plate or light fronts, starting from the positive and nega- 



glassy gelatino-broniide paper, and connected 

 with an electrostatic machine, will, especially if 

 the paper rest upon a piece of glass and this upon 

 a plate of metal, produce an effluvium round the 

 positive and a luminous globule at the negative 



tive carbons respectively, the positive one moving 

 with the greater velocity. This is accounted for 

 by the author on the supposition that the negative 

 ions move more slowly than the positive ions the 

 reverse of what happens in the case of dissociation 





point. When the globule has attained a certain by Rontgen rays. The greater velocity of the 



positive ions would not only explain the fact 

 observed by Brown, but also the greater fall of 

 potential at the positive pole. Mrs. Ayrton (Jour- 

 nal of the Institute of Electrical Engineers, 28, 

 p. 400), after many experiments to determine the 

 cause of the hissing of the electric arc, concludes 

 that it is caused by air coming in contact with 

 the crater, and is due to the carbon's burning 

 instead of volatilizing. 



Electric Conduction. Drude (Physikalische 

 Zeitschrift, Jan. 6) states that the view that me- 

 tallic electric conduction is due to the transporta- 

 tion of ions leads to a simple explanation of the 

 optical characters of metals. If the current be 

 regarded as due to the wandering of ions of con- 

 stant mass and constant charge, there must be 

 several kinds of these two at least. As the re- 

 sult of a mathematical investigation, he concludes 

 that the relative masses of the different kinds in 

 a particular metal may be determined from its 

 optical properties. In the case of nickel they are 

 as 9.45 to 1. The same writer (Annalen der 

 Physik, March) elaborates an electron theory of 

 metals. It is not necessary, he thinks, to attribute 

 ponderable mass to an electron in order to be able 

 to attribute kinetic energy to its motion, and a 

 certain inertia, as exhibited in the magnetic devia- 

 tion of cathode rays and the optical qualities of 

 metals. The absence of a ponderable mass at- 

 tached to the electron makes it possible to bring 

 metallic and electrolytic conduction under the 

 same theory. The assumption that the ratios of 

 charge to mass in the positive and negative elec- 

 trons respectively are two absolute constants in all 

 metals is not in agreement with the optical be- 

 havior of the latter. In gold and copper it is 

 necessary to assume the presence of bound elec- 

 trons, having a certain position of equilibrium in 

 the body, and bound to the material particles. It 

 is these bound electrons which play a part in 

 optical processes. The author assumes the exist- 

 ence of different kinds of electrons with various 

 charges, each a multiple of an elementary charge. 

 These movable electrons or " nuclei " obey the 

 kinetic theory of gases. Positive and negative 

 electrons do not coalesce, owing to their high 

 kinetic energy, as in the case of a comet which 

 never returns to the solar system. The author 

 investigates contact electricity and thermo-elec- 

 tricity, with the aid of his theory, and believes 

 that all galvano- and thermo-magnetic effects may 

 be explained and calculated with its aid. Lodge 

 (Philosophical Magazine, May) suggests that con- 

 duction in the metals is due to passage of isolated 

 charged corpuscles from one atom to the next. 

 This does not cause any chemical change, because 

 each atom on gaining one negative corpuscle loses 

 a similar one. In electrolytes, however, the charged 

 corpuscles drag their atoms with them, so that 

 chemical changes occur. Reinganum (Annalen der 

 Physik, June) finds that the ratio of the conduc- 

 tivities of a metal for heat and electricity re- 

 spectively may be calculated from the electro- 

 chemical equivalent and the velocity of gaseous 



size it detaches itself from the negative point 

 (which becomes dark), and travels over the plate 

 or paper, by a more or less irregular path, some- 

 times dividing as it travels, toward the positive 

 point. When it reaches this, all luminosity is ex- 

 tinguished and the charges disappear as if the ter- 

 minals of the machine had been connected by a 

 inductor. 



Discharge by Flame. Villard (Comptes Rendus, 

 Ian. 15) asserts that a flame placed in an electric 

 field acts as a bundle of Rontgen rays, cutting the 

 lines of force, and the gases produced by the com- 

 bustion are active like Rontgenized air. In the 

 absence of an electric field the flame is inactive 

 and the gaseous products, transported into an elec- 

 tric field, produce no discharge. It is as if in 

 ordinary air the incandescent particles gave out 

 cathode rays, while in a field they gave out Ront- 

 gen rays; or rather analogues to these. This way 

 of looking at the facts is believed by the author to 

 explain a very large group of phenomena, includ- 

 ing flame discharges, discharges by incandescent 

 bodies and phosphorus, the radiations given out by 

 electric sparks, especially from the cathode end, 

 discharge by ultra-violet light, the Edison effect 

 (current between the positive end of the filament 

 of a glow lamp and an electrode fused into the 

 lamp), and the production of ozone by flames, in- 

 candescent bodies, the electric arc and sparks, by 

 the oxidation of phosphorus in the cold, and by 

 radium. 



Spark Discharge. Ruhmer (Elektrotechnische 

 Zeitschrift, Feb. 22) finds two distinct forms of 

 discharge with a Wehnelt interrupter and a spark 

 gap between a point and a disk. At large distances 

 single strong sparks cross the gap, while at short 

 distances a curved flame crosses from the point to 

 the disk. At intermediate distances a large num- 

 ber of thin spark lines branch out from the point 

 and extend toward the disk like a brush. Every 

 one of the lines has a sinusoidal wave shape, due 

 to a spiral form of the spark path. By chrono- 

 photography it is seen that the sparks are similar 

 in outline, but are successively displaced in the 

 direction of the disk. West (ibid., Oct. 26, 1899) 

 has made a photographic analysis of spark dis- 

 charges from a Wehnelt interrupter by means of 

 a " mutograph " in which the film moved continu- 

 ously at a rate of 1 to 7 metres per second. The 

 sparks traveled along approximately the same 

 paths during successive discharges, but did not 

 succeed each other regularly. Their diameter is 

 not uniform, and they are frequently brighter in 

 the middle than at the ends. Some of the sparks 

 are double or multiple an appearance due to sev- 

 eral sparks in rapid succession, as shown by their 

 tracks. Continuous current sparks do not show 

 these doublings or branchings. Abraham and Le- 

 nioine (Comptes Rendus, Jan. 29) measure the 

 duration of the electric spark by a method already 

 devised by them to test for a retardation in the 

 disappearance of the Kerr phenomenon. The total 

 light emitted by the spark is less than 40 times 

 that emitted during the cessation of the Kerr 



effect, and as this latter has been proved not to hydrogen atoms. He obtains thus the value 



