for Dfl. 46.92. At this date the old-established firm was in other hands,
but continued to trade as ‘Dr Arthur Chevalier’, who died in 1872.
Brenni (II).
565 PLASTER MODELS (409) 3/4 19th C.
By J.G. Hofmann, Paris
Height of double cone 158; diameter of ends 81
Six models in plaster to represent sections of the ray surfaces in uniaxial
and biaxial biréfringent crystals. Polarization may be plane, elliptical,
or circular, and crystals can give a variety of configurations to the
patterns seen because of the different symmetries of crystals; triaxial,
uniaxial, trigonal, etc. As these symmetries are never easy to explain
mathematically to students, three-dimensional figures were made to aid
teaching.
565
566 BIREFRINGENT SPECIMENS (423) . before 1873
Collection of 51 transparent specimens of biréfringent material to show
polarizing effects. The mounts are of cork or wood. In green museum
box divided in 7 sections, 420 x 340 x 120. They have'paper labels;
descriptions in manuscript by Van der Ven. Both mahogany and oak
cells are 120 x 61. Ttyo examplll by J.G. Hofmann (see 567).
Categories: quartz, quartz cut at right-angles to optical axis, mica, glass',
aragonite, calcspar, tourmaline, selenite, et&;:G:
566
566
567 BIREFRINGENT SPECIMENS f§22) 1867-1875
Various makers: J.G. Hofmann, Paris; Optisches Institut von
Wilhelm Steeg, Homburg; P.J. Kipp & Zoon, Delft
Chest 360 x 260 x 110
Colletetion of 127 mineral preparations for démonstration of the polarization
properties of crystals. All containejSlin an oak chest with bottom
and three removable trays. The trays are divided into square cells to
contain the square preparation mounts.
Bottom. 35:'■•not signed 18; Hofmann 1; Steeg 11; retardation plates 5.
Tray 1. 34: not signed 13 ; Hofmann 1; Steeg 16; 4 items o f crystal in unmarked cork mounts.
Tray 2. 34: not signed 12; Hofmann 2; Steeg 14; 6 crystals in card mounts, with numbers only.
Tray 3:-24: /not signed 8 ; ^ Steeg 8. Also crystals in 8 pill boxes: Mj. KIPP & Z“ DELFT.