Pressure Phenomena of the Mucronate Anode

VOL. 13, 1927

PHYSICS: C. BAR US

503

The writer wishes to express his indebtedness to Prof. R. S. Mulliken, at whose suggestion the photography of the bands was undertaken, and who has on many occasions given valuable advice on various questions. * NATIONAL RsSZARCH FZLLOW. 1 W. Jevons, Proc. Roy. Soc., 91A, 120 (1914). 2 R. S. Mulliken, Physic. Rev., 25, 259 (1925). 3 F. Baldet, Compt. rend. Acad. Sci., 180, 820 (1925). 4M. Guillery, Zs. Physik, 42, 121 (1927). I R. S. Mulliken, these PROCZZDINGS, 12, 151 (1926); Physic. Rev., 28, 481, 1202 (1926); Ibid., 29, 391, 637 (1927). 6 F. Hund, Zs. Physik, 36, 657 (1926). 7R. S. Mulliken, Physic. Rev., 26, 561 (1925). 8 R. S. Mulliken, these PROCESDINGS, 12, 151 (1926). 9 E. Hulthen, Physic. Rev., 29, 17 (1927), (CaH bands); R, S. Mulliken, Ibid., 29, 637 (1927), (CaH, MgH). 10 R. S. Mulliken, Ibid., 28, 1219 (1926). 11 R. S. Mulliken, Ibid., 28, 481 (1926). The definitions and notation for the zsF quantities used here are those set forth in this article. 12 E. C. Kemble and F. A. Jenkins, Ibid., 29, 607 (1927). Abstract. 13 C. M. Blackburn, these PROCHEDINGS, 11, 28 (1925).

PRESS URE PHENOMENA OF THE MUCRONA TE ANODE* By CARiL BARUS BROWN UNIVURSITY,

PROVIDENCE, R. I.

Communicated June 11, 1927

1. Introductory.-The date of the preceding paper showed the pressures produced by a convection current emanating from the cathode, when its center is provided with a slightly projecting needle point. In the present experiments the mucronate electrode E (see Fig. 1, E,E' electrodes, n needle pt., b micrometer screw, interferometer U-gauge beyond U) is an anode. Let x be the width of the spark gap, y the projection of the needle, and s (roughly in 10-6 atm.) the pressure of the wind from n impinging on the perforated cathode E'. A small Winshurst, capable of delivery, 1/2 inch sparks energizes the posts P and P' and appurtenances. 2. Data.-The former results with the cathode point are recorded in figure 2 (for x = 2 cm.), for comparison. The cusp of the graph is often over s = 600 high. It differs, therefore, strikingly from the first of corresponding anode graphs, caet. par., figures 3 and 4, obtained consistently throughout many repetitions. There is no suggestion of a cusp for small y values, but the graphs rise leisurely to flat maxima. From these one would infer that an anode potential maximum is absent.

504

1i~ ~ V PHYSICS: C. BARUS

PROC. N. A. S.

However, in figure 5 for a spark gap x = 1 cm. the characteristic form reappears, though the graph seems to be made up of two roughly linear parts abruptly joined at A. One notes that if y = x, s = 0 nearly, which is also roughly the case in figures 3 and 6. The results of figure 5 led me to suspect that there might be something amiss in the apparatus which was, therefore, generally overhauled with the results shown in figure 6 curve A, though at times the form b was obtained from very slight interference with the apparatus. What the nature of the difference of figures 3 and 6 may be, I have been unable to detect; but since anything like sputtering or purring in the discharge

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is fatal to -high s values, and since this condition sets in casually, such occurrences are probably in question. The cusp in figure 6 is but slightly lower than in figure 2 for the cathode, though the former is much nearer the electrode. Figures 4 and 7 for x = 4 cm. show a similar change in the form of graph obtained. Again in figure 7 the cusp is rounded in the way also observed in the cathode curves. The crest, however, is now further away from the electrode, all of which illustrates the capriciousness of these sparking phenomena. If we join figures 2 and 6, reversing either one or the other, we get a diagram recalling to some extent the distribution of potential gradient or field strength in a vacuum tube, though in the present instance we are dealing merely with the convection currents between mucronate electrodes.

voL. 13, 1927

PHYSICS: BEAMS AND LA WRENCE

505

The great difficulty with the work is the fluctuating behavior of the machine, so that long observation is necessary to obtain the mean fringe deflection at each point. Thus it appears that sharp surfaces of max. and of min. potential, respectively, surround the anode and cathode, the surfaces confronting each other and about half a mm. from the electrode plates. If the needle point of the mucronate electrodes penetrates these limiting surfaces a convection current is observed whose strength decreases rapidly as the needle protrudes further. At the surface there is usually a cuspidal maximum of current. If the needle point lies within the surface, it is inert and spark discharge, sputtering or purring may occur between any points of the electrode, while the convection current is absent. In how far these results conform with the usual equations for space charges I have yet to learn. * Advance note from a Rep6rt to the Carnegie Institution of Washington, D. C. See these PROCBUDINGS.

ON THE LAG OF THE KERR EFFECT By J. W. BlAMS* AND ERNST 0. LAWRZNCZ3* YALE UNIV}RSITY Communicated June 7, 1927

Introduction.-Kerr discovered that certain liquids placed in an electrostatic field exhibit slight double refraction. The generally accepted explanation' of this phenomenon, called the Kerr effect, is that molecules possess definite optical anisotropy and that an electric field exerts an orientative influence on the molecules of the liquid, thereby giving rise to general optical anisotropy of the medium. Langevin originally assumed that the molecules are both optically and electrostatically anisotropic, the orientative action of the field arising from the couple exerted by the field on the electric moment induced along a preferential direction of the molecule. Born later took into account also the orientative couple of the electrical field due to the permanent moments of the molecules. A rather wide range of experimental facts indicate that this view of the mechanism of the Kerr effect is essentially correct. For example, Raman and Krishnan2 have recently shown that data on the scattering of light by liquids, which are measures of the optical anisotropy of the molecules, fit in very well with estimates of molecular optical anisotropy made on the basis of the orientation theory and Kerr effect data. Accepting the view that the orientation of the molecules by the electric