PHYSICS, PROGRESS OP, IN 1901. 



529 



the corpuscular charge causing a change of den- 

 sity in the ether surrounding it, this latter giving 

 the gravitational attraction." Grounds are ad- 

 duced for holding that (C) "gravitational force 

 is propagated at practically infinite velocity as 

 an expansional wave." 



Molecular Theories. J. J. Thomson (Paris 

 Physical Congress Report, 1900, 3, p. 138) elabo- 

 rates his new theory of subatomic corpuscles, 

 starting from an estimation of the mass of cath- 

 ode-ray corpuscles in which he concludes that 

 each has about -n&nj- the mass of a hydrogen atom. 

 We have thus, he says, a new state of matter, 

 consisting of corpuscles whose mass is the same, 

 no matter from what material they may be de- 

 rived. Each carries a fixed charge of negative 

 electricity. The corpuscular condition is pre- 

 sented not only in cathode and Lenard rays, but 

 also near a metal plate under ultra-violet light, 

 near a filament incandescent in a very high vac- 

 uum, and in the radiations from radio-active sub- 

 stances. The author thinks that it also exists 

 throughout metals and causes their conductivity. 

 Under an electric force, the corpuscles in the metal 

 move in an opposed direction with their charges, 

 and the metal appears to carry current. If they 

 travel to a cooler part of the metal, they carry 

 kinetic energy with them; whence thermal con- 

 ductivity. If we calculate on this theory the ratio 

 of the thermal to the electric conductivity, the 

 result is fairly in accordance with facts, but is 

 not quite conclusive; and the observed ratio is 

 not exactly the same in all metals, as it shauld be 

 on this theory. Each molecule of bismuth seems 

 to shed and reabsorb corpuscles about 40,000,000 

 times per second on the average; molecules of 

 other metals much oftener than this. W. Voigt 

 (Annalen der Physik, March) criticizes the older 

 views as to solids. He attacks the theory that the 

 behavior of a solid is expressible by a few con- 

 stants throughout its substance, including the 

 surface, and also objects to the application of the 

 laws of homogeneous strain without modification 

 to heterogeneous strain. The author concludes 

 that much searching experiment is needed before 

 a satisfactory theory of solids can be framed. 



Relations of Ether and Matter. Kelvin (Philo- 

 sophical Magazine, July), in discussing the rela- 

 tive motion of ether and ponderable bodies, sug- 

 gests that as Fresnel's and Young's hypotheses 

 are inconsistent with the elastic-solid theory of 

 ether, we may have to relinquish the doctrine that 

 two portions of matter can not jointly occupy the 

 same space. Ponderable bodies may then be as- 

 sumed not to displace ether as they move, while 

 each atom alters the density distribution of the 

 ether within the space which it occupies itself. 

 This hypothesis will explain (1) how matter can 

 act on ether so as to produce light, (2) why the 

 speed of light is less in transparent ponderable 

 matter than in pure ether, and (3) the aberration 

 of light. It is inconsistent, however, with Michel- 

 son and Morley's experimental conclusion that 

 ether in the earth's atmosphere is motionless rela- 

 tively to the earth unless indeed the motion of 

 ether through matter alters its linear dimensions. 

 In a subsequent article (ibid., August) the author 

 asserts that we have strong reason for believing 

 the density of ether to be constant throughout 

 space, and that this density (water being unity) 

 should be not less than 5 X 10~ 18 . He concludes 

 that ether and matter are not mutually exclusive, 

 but may freely occupy the same space, or inter- 

 penetrate each other. He also asserts that the 

 mean density of ponderable matter throughout 

 any very large spherical volume in space is less 

 the greater the radius. W. Wien (Archives Neer- 

 VOL. XLI. '34 A 



view that 

 H.I I work 



' revei-sal 

 of ;i pos- 



,tead 

 Tlio 



landaises, 5, p. 90, 1900) advance 

 the most promising direction for I'M 

 in mechanics and electricity lir in 

 of the usual methods, arid "the .-<< k 

 sible electromagnetic theory of mc<-!; 

 of a mechanical theory of electrom:i . 

 writer takes as fundamental the eon. 

 electric and magnetic polarizations 

 and develops his equations from this, a-iMinin" 

 also that mechanical phenomena are eleetnmmff 

 netic, and further that what is termed matter is 

 made up of the positive and negative elect ii<: 

 quantities or elements which we regard as the 

 convergence points of the lines of force. The ether 

 is regarded as at rest, and the electric quantities 

 are the only ones supposed to change position. 

 All forces are considered to be electromagnetic 

 and due to stresses in the ether. By different 

 groupings of positive and negative quantities at 

 different distances very complex effects may bo 

 obtained, and the author thus believes it possible 

 to reconcile Michelson's interference experiment 

 w r ith the theory of the ether at rest. For Lorentz 

 has shown that the length of a body in the direc- 

 tion of the earth's motion is shortened if the 

 molecular forces can be replaced by electrostatic 

 forces. Hence Michelson's result is explained, if 

 we can apply this to the molecular motions. L. 

 Graetz (Annalen der Physik, May 29), in an at- 

 tempt at a mechanical representation of electric 

 and magnetic phenomena, arrives at the conclu- 

 sion that in a vacuum ether behaves as an elastic 

 body. In ponderable bodies action takes place 

 between the disturbed ether and the molecules, 

 which action is electrostatic force, those parts of 

 a substance where it continues to exist being 

 ions. Magnetic polarization is the torsion of ether, 

 while electric forces, other than electrostatic, are 

 its translation velocities. The so-called true mag- 

 netization has neither existence nor meaning. 

 True electrification is the excess of the included 

 ether above the normal. Electric conduction con- 

 sists in the motion of molecules. The motions 

 of matter and ether are not independent. The 

 theory can easily be extended to explain the phe- 

 nomena of dispersion. 



Hardness. F. Auerbach (Annalen der Physik* 

 September, 1900) defines hardness for the case of 

 plastic bodies, including metals, by the limiting 

 pressure per unit surface attainable between a 

 lens and a plate of the same substance. He gives 

 the following table of the hardnesses of various 

 fairly well-defined metals, as compared with min- 

 erals : 



Steel 361 Quartz. 



Brass 107 Fluorspar. 



Gold 97) 



Copper 95 v Calcspar. 



Silver 91 I 



Aluminum 52 Boric acid. 



Lead 10 Gypsum. 



C. Benedicks (Zeitschrift fiir Physikalische 

 Chemie, April 2) notes that the hardness of steel 

 depends on the formation of a homogeneous solid 

 solution of carbide (C 2 Fe ) with iron, while in soft 

 steel the carbide is only mechanically mixed with 

 the iron. As in general a solvent expands only 

 slightly on dissolving small quantities of foreign 

 substances, such solution increases the number of 

 atoms present in a given volume, or the atomic 

 concentration (density -4- atomic weight). Bot- 

 tone has shown that for 24 pure metals the hard- 

 ness is proportional to the atomic concentration, 

 but, by Avogadro's law, atomic concentration in 

 gases determines their pressure, and analogy 

 therefore suggests that hardness in simple bodies 



