PHYSICS, PROGRESS OF, IN 1898. 



631 



0.1093 seem to indicate non-exactitude of the law, 

 " for," as he says, " although the exact values of the 

 .atomic weights of these two elements are not known, 

 it is certain that they are not so far apart as would 

 be implied by these values for the specific heats. 

 Results with gold and platinum and copper and 

 iron are similar. The author accounts for the di- 

 vergences from the law on stereochemical grounds, 

 .assuming peculiarities in the configuration of the 

 metallic atoms. That there are such differences he 

 thinks follows from the theory of Werner, of Zurich, 

 that isomerism in metallic compounds is to be ex- 

 plained on similar grounds to those now accepted 

 with regard to the constitution of the carbon com- 

 pounds. 



Mechanical Equivalent. Patterson and Guthe 

 (American Association) have reconciled recent 

 conflicting redeterminations of this constant by 

 measuring with great care the value of the ampere 

 in terms of the electro-chemical equivalent of silver, 

 using a large specially constructed electro-dyna- 

 mometer and employing the torque of a phos- 

 phor-bronze wire to equilibrate the counter-torque 

 due to the effort between the magnetic fields of the 

 stationary and movable coils. This eliminates the 

 effect of gravity. The result obtained was 0.0011192 

 gramme per ampere per second. This exceeds 

 Lord Rayleigh's value by \ of 1 

 per cent, and causes the discrep- 

 ancy between the results of Grif- 

 fiths and those of Rowland to dis- 

 appear. Bailie and Fery (Paris 

 Academy of Sciences, May 23) 

 have determined the mechanical 

 equivalent by a new method, by measuring the heat- 

 ing effect on a cylinder of copper fixed in a rotating 

 magnetic field. The value of J was thus found to 

 lie between 422 and 426. 



Equilibrium. Bruni (" Atti dei Lincei," October), 

 in a discussion of the thermodynamics of equi- 

 librium in systems of two and three components 

 having one liquid phase, comes to the following 

 conclusion : " If to- a system of two components 

 with only one possible liquid phase there be added 

 .a third component which does not combine with 

 the first two and is not isomorphous with them, the 

 curves expressing equilibrium of the same order 

 (curves of saturation in binary systems and cryohy- 

 dratic curves in ternary systems) are parallel. Only 

 in systems represented by the curve of the ternary 

 mixture the third added component exists mostly 

 in the solid phase." 



Boiling Point. The boiling point of liquid ozone 

 has been determined by L. Troost (Paris Academy 

 of Sciences, June 20) to be 119 C., the tempera- 

 ture being determined by means of an iron-con- 

 ^stantin thermo-couple. 



Leidenfrost's Phenomenon. Stark (Wiedemann's 

 "Annalen," June), by including in a telephone circuit 

 a hot metal plate 'with a drop in the spheroidal 

 state, shows that the drop performs, with respect to 

 the contiguous layer of vapor, oscillations due to 

 differences of surface tension between the hot and 

 cold portions. 



Measurement of Radiance. Angstrom has devised 

 an instrument for measuring radiance, which was 

 exhibited by E. S. Ferry to the American Associa- 

 tion. It consists essentially of two bolometer strips, 

 one of which is heated by the radiance to be meas- 

 ured and the other is heated to the same tempera- 

 ture by an electric current, from which the absolute 

 valve of the radiance may be calculated. 



Light, Velocity. Morby, Eddy, and Miller (A mer- 

 ican Association), from experiments to determine 

 whether the speed of light is affected by magnet- 

 ism, conclude that its velocity in carbon bisulphide 

 is not altered by one part in a hundred million by 



a magnetic field of such an intensity as to turn the 

 plane of polarization through 180 Q in a path of 85 

 centimetres. 



I'hotometry.Uood (" Science," June 3) describes 

 a form of flicker photometer consisting of a white 

 upright prism of 90 whose sides are illuminated 

 by the lights to be compared. Between this and 

 the observer is a cylindrical lens or biprism of small 

 angle, whose rapid oscillation causes the flicker, the 

 illuminated sides of the prism being presented to 

 the eye in very rapid succession. This instrument, 

 like other flicker photometers, is independent of 

 color. 



Transparency. Rubens and Aschkinass ( Wie- 

 demann's " Annalen," March) find that steam and 

 carbonic acid absorb infra-red rays of wave length 

 about 24 n in thick layers. Their absorption by the 

 atmosphere accounts for the absence of these rays 

 in the solar spectrum. Some liquids are very trans- 

 parent to the rays, especially benzol. 



Spectroscopy. Michelson" (" American Journal of 

 Science," March ; "Astrophysical Journal," June) has 

 devised what he calls the "echelon spectroscope," 

 which reveals details of the spectrum beyond the 

 power of the best gratings hitherto invented. In 

 this instrument spectra of a very high order are 

 used ; by building up a flight of glass steps, as in 



DIAGRAM OF PRISMS. 



the illustration, the difference in the optical path 

 for various sections of the light may be made any 

 desired number of wave lengths and a spectrum of 

 order 20,000 may thus be produced. In a descrip- 

 tion in " Science," Aug. 19, C. R. Mann says : 



"The blocks of glass composing this ' staircase ' 

 must be of exactly the same thickness, a -result 

 which is accomplished by polishing a plate of op- 

 tical glass until its opposite surfaces are plane and 

 parallel to each other, and then sawing this plate 

 into pieces of the requisite size. Suppose now a 

 beam of parallel light to fall on this pile of plates 

 perpendicular to the face at A. In passing through 

 the first block from a to b the beam will be retarded 

 by, say, 20,000 waves, the number depending on the 

 thickness and the index of refraction of the glass. 

 Part of the light then comes out into air through 

 the narrow opening be and the rest goes on through 

 the block cd. The part of the incident beam which 

 comes out through the opening de has also been re- 

 tarded 20,000 waves over the part that came through 

 be and so on. It is thus easily seen that this instru- 

 ment, when looked through along the axis from B 

 to A, gives the required conditions for the produc- 

 tion of a diffraction spectrum of high order; for 

 we have the light between the source and the point 

 of observation divided into a number of beams, each 

 of these beams having to travel 20.000 waves farther 

 to reach its goal than its adjacent beam on one side 

 of it, and 20,000 waves less than its adjacent beam 

 on the other side of it." 



With this instrument a resolving power of more 

 than 300,000 has been attained, and it is believed 

 that 500,000 will soon be reached. The highest 

 power of the best gratings is about 100,000. Of 

 course the field is extremely small. Perot and Fabry 

 (Paris Academy of Sciences, Jan. 3) have devised a 

 new form of interferential spectroscope composed 

 of two plates of silvered plane glass, producing 

 rings that are observed from an infinite distance. 

 Fabry and Perot (ibid.. May 31) find that the order 

 of an" interference fringe of high order, such as those 

 produced by two parallel silvered plates about 3 





