Sections can be obtained from Voight & Hochgesang, Göttingen; C. Marchand, rue Censier, 16ter, Paris; W. H. Tomlinson, Swarthmore, Pa., and G. D. Julien, 3 Webster Terrace, New Rochelle, N. Y. Footnote 125: Made by G. D. Julien, 3 Webster Terrace, New Rochelle, N. Y. Price: Power lathes (complete), $150.00 up; Foot-treadle lathes, $90.00 up. Footnote 126: A Crocker-Wheeler motor of ¼ to ½ H. P. will be large enough for an ordinary laboratory machine. Footnote 127: Made by Voigt and Hochgesang, Göttingen. Price, $15.00. Footnote 128: Saws charged with diamond dust can be obtained from Elisha T. Jenks, Middleboro, Mass. Price in 1910, $1.35 per diametrical inch. Foreign saws 6″ and 8″ diam. can be bought from G. D. Julien, New Rochelle, N. Y. Footnote 129: _School of Mines Quarterly_, Vol. XI, p. 32. Footnote 130: “Half a pound or less of ordinary shellac is melted in a flat-bottomed open vessel over a Bunsen burner. Then an equal quantity of Venice turpentine is carefully added under constant stirring. The mass should be allowed to boil for about ten minutes, during which the stirring is continued. Then small quantities are poured in separate heaps on an iron plate or other cold surface and rolled into sticks about seven inches long and half an inch thick.” Footnote 131: Square or standard 26 × 46 mm. glass slides are recommended instead of the oblong slides (1 × 3 inches), which are very apt to project beyond the edges of the stage and be struck by the fingers while rotating the stage. Footnote 132: Reference can be made to the publications on this subject by: Borichy, Behrens (Behren’s translation by Judd), Haushofer, Huysse, Klément, Streng, Rénard, etc. Footnote 133: In case an acid is to be used which would attack glass, the cover-glass can be replaced by a thin perforated disk of platinum. Footnote 134: The bases in solution can be determined by different methods of analysis, for which the student is referred to more elaborate works on this subject. In some cases it may be very advantageous to treat the section with acid, to remove certain soluble constituents, when other minerals not distinctly seen at first may be made more apparent. Footnote 135: The gas may be H_{2}S from a soluble sulphide, in which case the solution containing the bubbles will color filter paper moistened with lead water. Footnote 136: _Geol. and Nat. History Survey of Minn._, XIX., Ann. Rept., p. 42; also A. J. Moses, _Characters of Crystals_, p. 147. Footnote 137: The symmetry of the etched figures would, of course, be related to the system of crystallization. Footnote 138: A. J. Moses, _Characters of Crystals_, Chap. XVI. Footnote 139: When it is desired to preserve the section and at the same time to study the surface covered with a film of air, the edges alone of the cover-glass should be cemented. Footnote 140: