» Nicol Prisms (3) with relative support (0046)
Immagini
DESCRIPTION
The Nicol prim is a device to produce a beam of polarized light. Invented by William Nicol (1770-1851) in 1828 it was largely used in the 19th century to obtain polarized light from a beam of natural light. It is a rhomboidal calcite (Iceland spar) crystal cut such that the angle between the faces is 68° instead of the natural crystal plane angle 71°. The rhomboid is then cut in two, along a plane perpendicular to that of the two diagonals of the bases, and passing through the vertices of the two closer obtuse angles. The two parts are subsequently joined in the original position and glued together, with a small layer of Canada balsam, a monorefrangent substance of refractive index intermediate between the two indices of refraction of calcite which instead is birefringent. In the calcite there are two rays: ordinary, corresponding to the refractive index (1.6583) and extraordinary, corresponding to (1.4864) polarized in planes perpendicular to each other. The ordinary ray meets the surface of the layer of balsam under an angle greater than the angle limit; it is reflected and is then totally eliminated. The extraordinary ray passes beyond the prism, and substantially maintains the original direction. The beam leaving the prism is then polarized in a plane perpendicular to the main section. Placing two Nicol prisms in such a way as to have the planes of polarization crossed the incident ray is completely blocked. The prism support has a perforated rotatable disk which allows to select the opening through which the beam should pass. The instrument is so constructed as to be mounted on apparatuses more complex or on optical benches.ISCRIZIONI
- Sul supporto principale sono incise le sigle 'ELN' (logo della casa costruttrice Leybold Nachfolger) e '19'; sui tre prismi di Nicol sono incisi i numeri '20', '21', '22'.
- Sui due supporti per ottica della Foto 2 è inciso il numero 23.
Dati Catalografici
| Data di costruzione: | --- |
|---|---|
| Data di carico: | anteriore al 1874 |
| Nr. Inventario: | 682 (Generale dal 1874) |
| Costruttore: | Leybold Nachfolder |
| Materiale: | ottone, vetro |
| Dimensioni: | Supporto: diametro 8 cm, altezza 14,5 cm; Prismi: lato del rombo 1 cm, altezza 3 cm |
| Conservazione: | buono (Da inventario risultano 6 prismi, attualmente ne sono presenti solo 3) |