4C5 



ULTRAMARINE. 



UNDULATORY THEORY OF LIGHT. 



4C6 



States. As an emollient this bark is of great service as an external 

 application to wounds, bruises, chilblains, and cutaneous eruptions ; 

 for these it is generally made into a poultice. The bark of this tree 

 is probably that which is termed cortex unguentarius, which is in high 

 repute with the aborigines for the cure of wounds. 



ULTRAMARINE. This beautiful blue pigment was originally 

 made from the stone called lapis lazuli; and as the process was a 

 tedious one, the price was enormously high. The lapis lazuli was 

 analysed by Clement and Desormes ; and their analysis led Guimet 

 to the conception of producing artificial ultramarine. Other chemists, 

 including Gmelin and Hobiquet, devised other modes of attaining the 

 same end ; and now artificial ultramarine is a regular manufacture. 

 The substance is made largely in Germany, but not much in England. 

 One of the processes consists in taking equal parts of silica, sulphur, 

 and carbonate of soda, grinding them up into a bluish-green mass, 

 igniting them in the open air, and applying various finishing processes 

 to the bluish powder which results. The artificial ultramarine thus 

 produced is saleable at so low a price aa 1*. 3rf. per Ib. It is very 

 much cheaper than real ultramarine, and though inferior to that as a 

 pigment, is more beautiful than smalt ; hence it has come largely into 

 use. The scientific journals have lately given a description of the 

 ultramarine factory of Messrs. Zeltner and Heyne at Niirnberg, 

 the chief makers of this pigment. The buildings are said to cover 

 seven acres. The central building ia a polygon of 24 sides ; it has 

 12 compartments, 96 furnaces, 12 high chimneys, and 12 lines of tram- 

 ways. The polygon is 136 feet in diameter. In various parts of the 

 area are mills, steam-engines, washing apparatus, long ranges of drying 

 rooms, and store rooms for 5000 or 6000 cwts. of artificial ultramarine. 

 Two hundred persons are employed in this single manufacture. The 

 best kinds of artificial ultramarine, used only by artists, pass through 

 no less than eighty separate processes ; but the commoner kinds, 

 which are commercially more important, are coming largely into use 

 in paper staining, sealing-wax making, calico printing, colour printing, 

 and dyeing. 



According to the experiments of Dr. Eisner, ultramarine must con- 

 t-iin Hulphuret of iron as well as sulphuret of sodium, and he has given 

 the mean of several analyses of artificial ultramarine, of natural lapis 

 lazuli, and of an artificial product by Varentrapp : 



I'MUKK. [COLOURING MATTERS.] 



I M I!I LICUS. This word has sometimes been applied to the focus 

 of an ellipse ; but in modern works, it stands for a point of a surface 

 tlinij.'li which all its lines of curvature pass. At such a point the 

 two principal curvatures are equal ; but paint of ipherital cunatvn it 

 a better name. (' Differential Calculus,' ' Library of Universal Know- 

 ]. .!-<,' p. 440.) 



I ' M UK.V. The Latin word has been used to signify the shadow of 

 the earth or moon in an eclipse : the word penumbra is still retained 

 [ECLIPSE] to signify that portion of the heavens which is partially 



UMBRELLA, a shade carried over the head as a shelter from the 

 rays of the sun, or from rain and snow. Although the name is appli- 

 cable in either case, and perhaps most strictly in the former, the term 

 umbrella is usually applied in this country only to such of these 

 articles as are used as a protection against rain; while the name 

 parasol is given to the light kind of umbrella carried by ladies as a 

 defence from the heat of the sun. The French have a better dis- 

 tinction between the two kinds of umbrella; using the name parasol 

 for those used to ward off the rays of the sun, and parajiluie (from 

 /,lui' , rain) for those used as a defence against inclement weather. 

 Umbrellas were introduced into Europe, in comparatively recent times, 

 from the Kaxt, where they have been used for shelter against the sun 

 from time immemorial. Although pretty well known in London more 

 than a century since, they did not come into general use for many 

 years later. Jonas Hanway is said to have been one of the first men 

 who commonly used an umbrella in England. At first they were kept 

 in the halls of genteel houses, for holding over persons as they stepped 

 to their carriages ; and even long after they began to be used by 

 pedestrians, they were considered signs of effeminacy if carried by 

 males. Increased attention to comfort, and the reduced price of 

 umbrellas, owing to improvement in their manufacture, have now 

 rendered them almost as essential as articles of dress, even to the 

 hmnlile.it classes. 



The construction of common umbrellas, and the contrivances by 



which they are made to expand or collapse at pleasure, are too 



.irly known to need description ; and it is unnecessary to do more 



than niriitinn Home of the ingenious improvements which have- been 



ARTS AND SCI. HIV. VOL. VIII. 



devised. In umbrellas of the ordinary construction the ends of the 

 ribs are connected with the fixed ring upon the end of the stick, and 

 the ends of the metallic rods called stretchers are attached to the 

 sliding-tube, by rings of wire ; so that the axes upon which they turn 

 when the umbrella is opened and closed form arcs of a circle, instead 

 of straight lines, by which excessive friction and destructive wear are 

 occasioned. The outer ends of the stretchers, also, are connected with 

 the ribs by means of axes or pins passed through the latter, by which 

 they are so weakened that they frequently break. These defects are 

 remedied in some modjern umbrellas, by the adoption of ingenious 

 though simple joints. Another new kind has a joint for connecting 

 the stretchers with the ribs, allowing the framework to collapse into 

 less space than usual, and preventing the fretting or wear of the cover 

 at the ends of the stretchers. Very light and compact umbrellas are 

 made with ribs of steel instead of whalebone or cane, which latter 

 material, stained to resemble whalebone, is used in those of the com- 

 moner sort ; and some of the best umbrellas and parasols are made 

 with hollow or tubular metallic sticks, which combine lightness with 

 strength. 



In some of the umbrellas of recent invention, the ribs, sticks, strips 

 and fillets are made of vulcanised india-rubber, a very tough yet 

 elastic material. In Fox's patent umbrellas the ribs and stretchers are 

 made of thin steel bent into the form of a hollow trough, by passing 

 strips of metal between suitably shaped rollers, and annealing them 

 frequently ; the ribs and stretchers are thus made very strong although 

 light, and their ends are properly shaped between steel dies. By 

 Holland's patent, the ribs are made of elliptical hollow tubes. Mr. 

 Pitton makes telescopic handles, and steel ribs with a folding hinge 

 or joint. Many firms at Birmingham carry on the manufacture of 

 umbrella furniture on a large scale, employing machines for every 

 part of the work ; even the little hinges which allow the handles of 

 parasols to be folded are made to the extent of severals tuns yearly. 



UMBRIAN SCHOOL OF PAINTING. [PAINTISO.] 



UMPIRE. AWARD. The word umpire is sometimes used to 

 denote the person who in the first instance decides a controversy ; but 

 in its legal sense it means a person named in the Submission, or under 

 its authority, by the arbitrators [ARBITRATION] to decide the matters 

 referred, which the arbitrators either cannot or will not decide. 



The rules which govern an arbitrator regulate the conduct of the 

 umpire also. If -arbitrators agree upon certain matters referred to 

 them, but are unable to agree upon others, the umpire may adopt and 

 incorporate in his umpirage the former, and may himself decide upon 

 the latter. If again arbitrators are unable to decide upon matters 

 concerning which they have heard the evidence, they may report that 

 evidence to the umpire, and his award thereon will be good, provided 

 that before it was delivered neither party required of him to hear the 

 evidence afresh. 



the 



talks of " that admirable invention of Mr. Newton, whereby he deter- 

 mines the Undo:, or numbers prefixed to the members composing 

 powers," meaning to speak of what we should now call the numerical 

 coefficients, which enter in any particular case of the binomial 

 theorem. 



UNDECAGON, a figure of eleven sides. 



UNDETERMINED (Mathematics), not known, as distinguished 

 from indeterminate, which cannot be known. Thus, " What numbers 

 are those whose sum is 100 ? " is indeterminate : many numbers will 

 satisfy the condition, but the problem contains no mode of distinguish- 

 ing the answer which is wanted, nor of giving a preference to one 

 answer over another. But an undetermined quantity may be deter- 

 minate, or capable of being determined. There is, however, fre- 

 quently a want of proper distinction in the use of these words. 

 [INDETERMINATE.] 



UNDULATORY THEORY OF LIGHT, a theory in which it is 

 attempted to explain the phenomena of light by the supposed vibra- 

 tions of an ethereal medium. 



Descartes is considered as the first who entertained the opinion that 

 vision might be so explained ; but that philosopher only states that 

 light may be a certain movement or action of the molecules of air and 

 other pellucid substances. He supposes that the effects may be 

 instantaneously transmitted to the eye ; and he compares the appre- 

 hension of external objects by vision to that which a blind man obtains 

 when, holding a staff at one of its extremities in the hand, the opposite 

 extremity comes in contact with an obstacle. (' Dioptrices,' cap. 1.) 

 Mallebranche appears to have conceived th it there existed an analogy 

 between the phenomena of sound and those of light ; ascribing the 

 former to vibratory movements of the particles of air, and the 

 latter to the like movements of the particles of an ethereal medium 

 between the luminous body and the eye. But Huygens (' Tractatus 

 de Lumine ') both advanced the undulatory hypothesis and explained 

 by it the laws of reflection and refraction of light, not only for ordinary 

 media, but also for Iceland spar, which possesses a powerful double 

 refraction. Newton, however, adopted the corpuscular theory, having 

 been influenced it would seem chiefly by the difficulty of accounting 

 fur the rectilinear propagation of a pencil of light, and the existence 

 of shadows, on the undulatory hypothesis. The great reputation of 



li u 



