Horizontal optical prism mounted on a stand to permit height adjustment

56.8 x 36 x 12.5
Carved and inlaid wood, glass and brass

INDEX 1788 : V.III.322

Machina similis descriptae, n.º 303, quae constat basi lignea, cui insistunt nae parastatae trochleis ad summa capita instructae. A parallelogrammo ligneo sustinetur Prisma crystallinum situ ad horizontem parallelo.

Instrument similar to n.º 303, consisting of a wooden base which has two columns with pulleys at the top. A glass prism is mounted horizontally in a rectangular wooden frame.

This instrument comprises a wooden base with two vertical columns at the top of which are two pulleys which use weights to hold a wooden frame containing a prism. The prism is equilateral and can turn on its axis. The regulating weights consist of two small pans which hold enough lead pellets to maintain equilibrium. The pans are suspended on cords that pass over pulleys, the other ends being fastened to the frame of the prism.

From Colégio dos Nobres, catalogue n.º 312.

's Gravesande, Willem Jacob, Physices Elementa, Leiden, 1742, Tomo II, § 3524, Tab. CXII, Fig. 3.

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