In the course of his well-known investigations concerning the compressibility of gases and liquids, Amagat made some series of measurements taking observations through two small glass windows fitted to his high-pressure bomb (“méthode des regards”),* and he also twice made an attempt to use a similar arrangement for the determination of melting and crystallization at high pressures. His first paper on these subjects deals with the melting and with the formation of two different kinds of crystals of carbon tetrachloride. The highest pressure employed was 1,160 atmospheres. The second paper, in which a somewhat different arrangement of the glass windows was used, deals with the crystallization of ice at temperatures below zero under the influence of high pressures.^ In a summarizing paper Amagat§states that he occasionally was able to reach pressures of about 1,600 atmospheres before the glass windows were broken, but observations were not actually made at higher pressures than 1,000 atmospheres. In this paper a sketch of the apparatus is also given. Amagat states that he met with severe difficulties during these investigations, and he has not pursued the subject further. Later melting-points and transition-points of some “liquo-crystalline” substances have been measured in Jena glass tubes up to 300 atmospheres by Hullett, and other optical observations at pressures above that of the atmosphere have been made by Rothmund (maximum 500 atmospheres), Röntgen and Zehnder, Sierstema, Liveing and Dewar, Hutton and Petavel,§§ and Duffield, but in these investigations the pressures have, as a rule, not exceeded 100 atmospheres.