INDEX 1788 : V.II.325

Prismata duo ex crystallo Galico, quorum extrema capita sunt armata cochleis, ut Pedi (n.º 321) ligneo aptari possint.

Two prisms made from French glass with screws to hold them on a wooden stand (n.º 321).

According to the Index, these two prisms are made of French glass with brass fittings and pegs at the ends to hold them in the grooves of the stand n.º 321 (instrument 93). Each prism is 27.5 cm long. A section of one forms an isosceles triangle with a base measuring 2.5 cm and the sides 1.4 cm; a section of the second also forms an isosceles triangle, with a base measuring 2.7 cm and sides of 1.7 cm.

From Colégio dos Nobres, catalogue n.º 315.

's Gravesande, Willem Jacob, Physices Elementa, Leiden, 1742, Tomo II, § 3524, Tab. CXII, Figs. 2, 4 e 5.