Speculum metal

Spiegelmetall, n. speculum metal, spiegeln, v.t. reflect. — v.i. reflect, shine, glitter. — v.r. be reflected. — spiegelnd, p.a. reflecting. specular, shining. 

The reflecting stereoscope is not open to any single practical or theoretical objection. As an optical instrument it is absolutely perfect, being subject to no defects of distortion or aberration. For any scientific purpose, therefore, the reflecting stereoscope should always he preferred to the Other. The reflectors may be made of polished speculum metal if objection be raised to glass mirrors, and the pictures may he taken simultaneously in a camera with double lenses two and a half inches from centre to centre. 

Figure 23 is a cross-section drawing of the Fery pyrometer made by the Taylor Instrument Cos. Radiation from the source sighted upon is concentrated by the concave mirror of speculum metal or gold, upon the hot iunct on of a mimito tbprmo-... 

THn plates are thin sheets of Fe, coated with Sn. Tin foil consists of thin laminae of Sn, frequently alloyed with Pb. Copper and iron vessels are tinnml, after brightening, by contact with molten Sn. Pewter, bronze, bell metal, gun meUd, britannia metal, speculum metal, type metal, solder, and fusible metal contain So. 

Speculum metal (Latin speculum, a mirror) or white bronze contains 2 of copper and i of tin. It is whiter even than tin, extremely brittle, and takes a high polish. It was used in Roman days for making mirrors and in more recent times found application in reflectors for telescopes. Later it was, of course, replaced by the well-known silvering process (p. 116). 

Bronze is composed of about 90 parts of copper to 10 of tin bell-metal and gong-metal, of 80 parts of copper to 20 of tin. Speculum metal, for telescopes, is formed of 2 parts of copper and 1 of tin, with a little arsenic. 

The usual grating consists of a glass or speculum-metal sheet with a very large number of equidistant parallel lines ruled on it (usually of the order of 1000 per mm). Dif-... 

Simple ruled Diarmnd points on speculum metal or glass Diarmnd points onto copper Diarmnd points onto aluminum sputtered onto optically flat glass Harrison GR (1949) Journal of the Optical Society of America 39 413 (historical review) Wood RJ (1944) Journal of the Optical Society of America 34 509. Wood RJ (1937) Nature 140 723. 

The fact that the composition of the speculum deposit must be closely controlled to obtain the best results has been a serious drawback to development. The coating finds uses on decorative hollow-ware, oil lamps and tableware. The bronze deposits with 10 or 20% tin are used lacquered in decorative metal-ware for domestic and personal ornament and, in thick layers to protect hydraulic pit props against corrosion and abrasion. They have also been used with success as undercoatings for nickel-chromium or tin-nickel alloy deposits. 

To revert to the subject of the seed of metals, from the Speculum of Arnaud de Villeneuve come these words There is in Nature a certain fine essence, which being discovered and brought by art to perfection converts to itself proportionately all imperfect bodies that it touches, so that the first matter of all metals and substances is a fixed something altered by the diversities of place, temperature, etc. This Essence has always been recognized by alchemists as the Seed of Metals. 

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