Glass is lighter, stiffer, less costly and easier to work than speculum metal.
Francois and Speculum perfectionis, and Lempp's Frere Elie de Cortone.
The use of the convex lens, which is given as a great secret, in place of the concave speculum of the first edition, is not so clearly described as by Barbaro; the addition of the concave speculum is proposed for making the images larger and clearer, and also for making them erect, but no details are given.
It was very popular during the middle ages, and was used by Ordericus Vitalis for his Historiae ecclesiasticae; by William archbishop of Tyre, for his Belli sacri historia; and by Vincent of Beauvais for his Speculum historiaae.
D'Alengon (1906); the so-called Legenda trium sociorum; the Speculum perfectionis, discovered by Paul Sabatier and edited in 1898 (Eng.
Rogeri Baconis Anglici de Arte Chymiae Scripta (Frankfort, 1603) - a collection of small tracts containing Excerpta de Libro Avicennae de Anima, Breve Breviarium, Verbum Abbreviatum, 3 Secretum Secretorum, Tractatus Trium Verborum, and Speculum Secretorum; (5) Perspectiva (1614), which is the fifth part of the Opus Majus; (6) Specula Mathematica, which is the fourth part of the same; (7) Opus Majus ad Clementem IV ., edited by S.
Thus in the Speculum Naturale of Vincent of Beauvais (c. 1250) it is said that there are four spirits - mercury, sulphur, arsenic and sal ammoniac - and six bodies - gold, silver, copper, tin, lead and iron.
Simon's history, in its original form, is lost; but large sections of it have been preserved in Vincent of Beauvais's Speculum historiale, where nineteen chapters are expressly said to be ex libello fratris Simonis, or entitled frater Simon.
In these instruments the lines are ruled upon a spherical surface of speculum metal, and mark the intersections of the surface by a system of parallel and equidistant planes, o; of which the middle member passes through the centre of the sphere.
Rutherfurd introduced into common use the reflection grating, finding that speculum metal was less trying than glass to the diamond point, upon the permanence of which so much depends.
It is notable that an important instrument of research, the speculum, which has been reinvented in modern times, was used by Soranus; and specimens of still earlier date, showing great mechanical perfection, have been found among the ruins of Pompeii.
The sun shining, he fixed a round glass speculum (orbem e vitro) in a window-shutter, and then closing it the images of outside objects would be seen transmitted through the aperture on to the opposite wall, or better, a white paper screen suitably placed.
He discloses as a great secret the use of a concave speculum in front of the aperture, to collect the rays passing through it, when the images will be seen reversed, but by prolonging them beyond the centre they would be seen larger and unreversed.
He describes some entertaining peep-show arrangements, possibly similar to Alberti's, and indicates how the dark chamber with a concave speculum can be used for observing eclipses.
The Speculum Majus, the great compendium of all the knowledge of the middle ages, as it left the pen of Vincent, seems to have consisted of three parts only, viz.
The Speculum Naturale, Doctrinale and Historiale.
All the printed editions, however, consist of four parts, the additional one being entitled Speculum Morale.
The Speculum Naturale fills a bulky folio volume of 848 closely printed double-columned pages.
The Speculum Naturale is so constructed that the various subjects are dealt with according to the order of their creation; it is in fact a gigantic commentary on Genesis i.
The Speculum Doctrinale, in seventeen books and 2374 chapters, is a summary of all the scholastic knowledge of the age and does not confine itself to natural history.
Deals with physics and may be regarded as a summary of the Speculum Naturale.
As the fifteenth book of the Speculum Doctrinale is a summary of the Speculum Naturale, so the Speculum Historiale may be regarded as the expansion of the last book of the same work.
One remarkable feature of the Speculum Historiale is Vincent's constant habit of devoting several chapters to selections from the writings of each great author, whether secular or profane, as he mentions him in the course of his work.
One main fault of the Speculum Historiale is the unduly large space devoted to miracles.
The number of writers quoted by Vincent is almost incredible: in the Speculum Naturale alone no less than 350 distinct works are cited, and to these must be added at least 100 more for the other two Specula.
The so-called first edition of the Speculum Majus, including the Speculum Morale, ascribed to Johann Mentelin and long celebrated as the earliest work printed at Strassburg, has lately been challenged as being only an earlier edition of Vincent's three genuine Specula (c. 1468-70), with which has been bound up the Speculum Morale first printed by Mentelin (c. 1 473-7 6).
Boutaric, Examen des sources du Speculum historiale de Vincent de Beauvais (Paris, 1863), and in tome xvii.
With few exceptions all the known events of Defoe's life are connected with authorship. In the older catalogues of his works two pamphlets, Speculum Crapegownorum, a satire on the clergy, and A Treatise against the Turks, are attributed to him before the accession of James II., but there seems to be no publication of his which is certainly genuine before The Character of Dr Annesley (1697).
P. 419) suggested the division of the small speculum of a Cassegrain telescope and the production of double image by micrometric rotation of the semispecula in the plane passing through their axis.
Before it was a marvellous mirror erected on a many-storeyed pedestal (described in detail); in this speculum he could discern everything that went on throughout his dominions, and detect conspiracies.
His speculum metal is composed of four atoms of copper (126.4 parts) and one of tin (58.9 parts), a brilliant alloy, which resists tarnish better than any other compound tried.
In Brewster's Edinburgh Journal of Science for 1828 he described his machine for polishing the speculum, which in all essential points remained unaltered afterwards.
It imitates the motions made in polishing a speculum by hand by giving both a rectilinear and a lateral motion to the polisher, while the speculum revolves slowly; by shifting two eccentric pins the course of the polisher can be varied at will from a straight line to an ellipse of very small eccentricity, and a true parabolic figure can thus be obtained.
The speculum lies face upwards in a shallow bath of water (to preserve a uniform temperature), and the polisher fits loosely in a ring, so that the rotation of the speculum makes it revolve also, but more slowly.
In September 1839 a 3-foot speculum was finished and mounted on an altazimuth stand similar to Herschel's; but, though the definition of the images was good (except that the diffraction at the joints of the speculum caused minute rays in the case of a very bright star), and its peculiar skeleton form allowed the speculum to follow atmospheric changes of temperature very quickly, Lord Rosse decided to cast a solid 3-foot speculum.
By forming the bottom of the mould of hoop iron placed on edge and closely packed, and the sides of sand, while the top was left open, Lord Rosse overcame this difficulty, and the hoop iron had the further advantage of allowing the gas developed during the cooling to escape, thus preventing the speculum from being full of pores and cavities.
This invention secured the success of the casting of a solid 3-foot speculum in 1840, and encouraged Lord Rosse to make a speculum of 6 ft.
In the New English Dictionary the earliest example of the word " classical " is the phrase " classical and canonical," found in the Europae Speculum of Sir Edwin Sandys (1599), and, as applied to a writer, it is explained as meaning " of the first rank or authority."
Or reg.) of the 6th century, a palimpsest which once belonged to the monks of Fleury, and by the so-called speculum (m) or collection of quotations formerly attributed to Augustine but probably connected with Spain.
After him Kaikobad, son of his brother Faramarz, entered Konia as sultan in 1298, but his reign is so obscure that nothing can be said of it; some authors assert that he governed only ' See the details in Vincent of Beauvais, Speculum Historiale, bk.
Trans., The Sanctuary of the Faithful Soul, London, 1905); all these three works were translated and edited by Father Bertrand Wilberforce, O.P., and have been reprinted several times; and especially Speculum Monachorum (French trans.
Dee's Speculum or mirror, a piece of solid pink-tinted glass about the size of an orange, is preserved in the British Museum.
Specularia Speculum: hardy, 6 in., reddish-violet; free-flowering.
Among them the Vinland sagas, also a Norwegian work of the 13th century, called Speculum regale (The King's Mirror), and some papal letters, give interesting glimpses of the life of this colony.
Foucault invented in 1857 the polarizer which bears his name, and in the succeeding year devised a method of giving to the speculum of reflecting telescopes the form of a spheroid or a paraboloid of revolution.
No further practical advance appears to have been made in the design or construction of the instrument till the year 1723, when John Hadley (best known as the inventor of the sextant) presented to the Royal Society a reflecting telescope of the Newtonian construction, with a metallic speculum of 6-in.
Such speculum metal is exceedingly hard and brittle, takes a fine white polish, and when protected from damp has little liability to tarnish.
Xliv., February 1857), proposed to employ glass for the specula of telescopes, the reflecting surface of the glass speculum to be covered with silver by Liebig's process.
The best speculum metal and the greatest care are no guarantee of freedom from tarnish, and, if such a mirror is much exposed, as it must be in the hands of an active observer, frequent repolishing will probably be necessary.
Every time, therefore, that a speculum is repolished, the future quality of the instrument is at stake; its focal length will probably be altered, and thus the value of the constants of the micrometer also have to be redetermined.
Silvered mirrors have also some advantage in light grasp over those of speculum metal, though, aperture for aperture, the former are inferior to the modern object-glass.
Similar absorptions no doubt account for the disappearance of the Culdees of York, a name borne by the canons of St Peter's about 925, and of Snowdon and Bardsey Island in north Wales mentioned by Giraldus Cambrensis (c. 1190) in his Speculum Ecclesiae and Itinerarium respectively.
In 1578 was published the Speculum orbis terrarum of Gerard de Jude or de Judaeis.
At the present time excellent reproductions of Rowland's speculum gratings are on the market (Thorp, Ives, Wallace), prepared, after a suggestion of Sir David Brewster, by coating the original with a varnish, e.g.
Comparisons of light grasp derived from small, fresh, carefully silvered surfaces are sometimes given which lead to illusory results, and from such experiments Foucault claimed superiority for the silvered speculum over the object-glass.