The London, Edinburgh and Dublin philosophical magazine and journal of science . the central spine of ahexagonal crystal like (a) was formed. Then by certainchanges in the oven conditions the side branches grew outfrom the central spine as shown. Those in (c) were regu-larly developed hexagonal needles, which transmitted littleor no light. But the branches in (d) wrere thin plates, withacute angles of about 65°. As described in a previous paper(loc. cit.) these crystals transmitted a deep red light whenplaced between crossed nicols. Likewise they showedextinction parallel to the long axis of t
The London, Edinburgh and Dublin philosophical magazine and journal of science . the central spine of ahexagonal crystal like (a) was formed. Then by certainchanges in the oven conditions the side branches grew outfrom the central spine as shown. Those in (c) were regu-larly developed hexagonal needles, which transmitted littleor no light. But the branches in (d) wrere thin plates, withacute angles of about 65°. As described in a previous paper(loc. cit.) these crystals transmitted a deep red light whenplaced between crossed nicols. Likewise they showedextinction parallel to the long axis of the crystal. In some * Communicated bv the Authors. t G. W. White, Phil. Mag. [6] xxvii. p. 370 (1914). X F. C. Brown, Phys. Rev. n. s. 1914. Phil. Mag. S. 6. Vol. 28. No. 166. Oct. 1914. 2 K 498 Profs. F. C. Brown and L. P. Sieg on the Seat of forms like (c) and (d) the branches grew entirely togetheras the crystals developed, so as to form an apparently planesurface. They sometimes formed a solid lamellar crystalform, and were then excellent reflectors of large t cm. The form (e) is made up of four rows of branches placed90° apart. A large number of other crystal forms havebeen described (loc. cit.), all of which are , the forms described in this paper were best adaptedtojthe argument. Fig. 2. frton/T 4- P c c \ T= r 4^ fl ^T ^ fji II v II R C-j 1 o L \ o ~S Back This crystal was laid on a glass plate, Gr, and silver elec-trodes, P, P, were pressed against the upper surface of the Light Action in Certain Crystals of Metallic Selenium. 499 crystal by screws, S, as shown in fig. 2. The whole wasmounted on a hard rubber plate, R. With the crystal placedin this manner there was not much change in the conductanceon altering the pressure at the contacts. In view of thevery large change in conductance which was observed whenthe entire region between the electrodes was placed under afew atmospheres pressure, and in view of the well-knownchange
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectscience, bookyear1840
