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Former Display Label - The 'Universal Lamina'

The 'Universal Lamina'

The 'Universal Lamina' described in the Libros del saber (c.1277) of Alfonso el Sabio, of Castile, was probably invented at Toledo in the 11th century by the astronomer Abû-l-Hasan `Alî b. Khalaf ibn Ahmad. It was a precursor of the az-Zarqellu projection (the saphæa arzachelis; see the label on the right), also developed in Muslim Toledo in the 11th century. It reappeared in Europe in the 16th century as the 'Mathematical Jewel' of John Blagrave.

The maghribî astrolabe of 728 A.H. [= 1327-8 A.D.], displayed above, is a very rare example of a 'Universal Lamina'; it differs somewhat from the instrument described in the Libros del saber. The only other example known of an Islamic 'Universal Lamina' is the astrolabe by Ahmad b. Abî Bakr of 729 A.H., in the Benaki Museum, Athens; there is a Blagrave 'Mathematical Jewel' in the Adler Planetarium, Chicago.

The 'Universal Lamina' is a combination of an {ain}ankabût, similar to that of a conventional astrolabe, super-imposed on a universal projection of the type used by az-Zarqellu. The {ain}ankabût is usually divided into two halves along the E. -W. line, the tracery in the upper half representing almucantars and azimuths, that in the lower half being part of the usual stereographic projection, on the plane of the Equator, of the ecliptic and certain fixed stars. The outer circle of the `ankabût represents the Equator and not, as on a conventional `ankabût, the Tropic of Capricorn. In the example shown here, the almucantars and azimuths usually found in the upper half, have been replaced by the second half of the ecliptic circle and a further selection of fixed stars. The so-called Zarqellu projection below the `ankabût is of the usual type, to which have been added azimuth circles, as on a normal astrolabe plate for latitude 90°. The result is that for certain operations it is convenient to use the `ankabût, at the same time considering the Zarqellu projection as an ordinary plate for latitudes 0° & 90°; and for other operations to use the universal projection and to ignore the `ankabût. The `ankabût of this instrument is made for 58 stars.

The astrolabe is signed, on the back in the upper left-hand quadrant, 'Made by `Alî b. Ibrahîm al-Harrar, the muezzin, in Tâzà [Morocco], God protect her, in the year 728 [A.H. = 1327-8 A.D.]'. No other instruments by this maker have been recorded. Brass.

[For a description of the back, see the other side of this label.]

Purchased, in 1957, with a grant from Lord Leigh's Fund

Brass. Signed, on the back in the upper left-hand quadrant, 'Made by {ain}Alî b. Ibrahîm al-? Jazzâr, the muezzin, in Tâzà [Morocco], God protect her, in the year 728 [A.H.]'. No other instruments by this maker have been recorded.

On the back shown above, are a zodiac/calendar scale (0° Aries = 13.5 March; concentric type); an unequal-hour diagram; a sine and cosine graph; a shadow-square; and the usual scales of degrees. The alidade, of typical maghribî type, has declination scales engraved on the arm. The kursî, though of the low type associate with maghribî astrolabes, appears to be directly descended from the type of kursî found on the earliest Islamic astrolabes (of Syro-Egyptian origin).

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