48< ARCADE. 



7,851,963 inches, wrong only by one part out of 3890. Therefore, for 

 every practical purpose, an arc of a circle (and the same may be said of 

 every other curve) is the polygon made by the chords of a moderate 

 number of subdivisions of the arc. 



The preceding property is (but in what manner our limits will not 

 permit us to show) a consequence of the following proposition. Let 

 there be a number of arcs, such as A c B, cut off the same curve, having 

 their chords parallel to the tangent x c Y ; then, as A B moves parallel 



ARCH. 



486 



to its first position towards x y, c D not only decreases without limit 

 but its proportion to A B decreases without limit ; that is, let any num- 

 ber, however great, be named, then shall A B, before it reaches x Y, 

 reach a position in which it contains c D more than that number of 

 times. This proposition is startling to the beginner in mathematics. 

 and should be considered by him with great attention. It may be 

 illustrated in the following manner : Suppose that while A B moves 

 from its first position towards x Y, and has reached a 6, a miscroscope 

 moves with and over it, which increases in magnifying power as a b 

 moves, in such a manner that a b always appears in the glass as large 

 as A B to the naked eye. Then a c b will not be magnified into the 

 form A c B, but into A Q B, where <j D grows less and less without limit, 

 as a* approaches towards XY. But if two straight lines had been 

 taken, as in the following figure, a b could not have been magnified to 

 A B without changing a c 6 into ACS. 



Formerly, the term arc was frequently confounded with angle, 

 which arose from the practice of measuring angles by arcs of the 

 circle. For such terms as ABC OF ELEVATION, 4c.. we refer to ANGLE 

 OF ELEVATION, ftc. 



ARCADE signifies a series of arches on insulated piers, forming a 

 screen, and also the space inclosed by such. This in, perhaps, a limita- 

 tion of the term within that usually given to it ; but arcade is properly 

 a correlative of colonnade, and should not therefore have a more 

 extensive signification. What, by a strange perversion of the term, 

 are in this country called piazza*, and most particularly the part so 

 termed of the buildings in Covent Garden, London, are strictly arcades ; 

 and the market within the inclosed area of that same place or square, 

 U> which the term piazza properly applies, exemplifies, in a great part 

 of its exterior, the correlative term colonnade. 



In Gothic architecture the term arcade is applied to a series of arches 

 supported on piers, and used aa decorations for the walls of churches, 

 and occasionally of other buildings. The arches are sometimes open, 

 but more commonly closed by the masonry of the wall. Good examples 

 of arcades of the Norman and Early English styles (in which arcades 

 are most employed) occur in Canterbury cathedral ; of the decorated 

 style in Lichfield cathedral : but most of our cathedrals possess some 

 examples. 



In addition to its proper technical meaning, this term has acquired 

 .1 different signification among us as the popular name for what the 

 Parisians more properly designate a ' passage ' or ' galerie," namely, an alley 

 lined on each side with shops, and roofed over so as to be in fact a sort 

 of ' in-dcor ' street, entirely protected from the weather, and of uniform 

 design throughout in its architecture. So far, an arcade answers to 

 the idea of a bazaar, the chief distinction between the two being that 

 the latter has not so much of street character about it, but consists 

 either of a single spacious hall or separate rooms, fitted up with 

 counters and stands, and may therefore be likened to a single large 

 shop occupied by a number of different dealers, whereas in an arcade 

 the shops are quite distinct from each other, and enclosed in front with 

 windows after the usual manner ; and they have besides dwelling 

 accommodation, kitchen, &c., beneath, and a chamber over them, with 

 the addition sometimes of an entresol. Another distinction is that an 

 arcade serves as a public thoroughfare for foot-passengers. The Bur- 

 lington Arcade, which was the first place of the kind in London, has 

 indeed little more than its convenience as a thoroughfare and prome- 

 nade for foot-passengers to recommend it, inasmuch as it makes nu 

 pretensions to elegance of design, nor has it anything in accordance 

 with the title bestowed on it, it being neither arcaded in any way nor 

 arched over. The Lowther Arcade in the Strand (erected 1831) mani- 

 fests a great improvement upon that first specimen, for it is really a 

 handsome piece of architecture; the side elevations are divided by 



pilasters into compartments, each of which contains a shop-front, with 

 an ornamented triple window over it, and above that a semicircular 

 one in the arched head of the compartment. On the plan, each of 

 these divisions is covered by a peudentive dome with a circular sky- 

 light ; and these numerous domes and their arches produce a pleasing 

 perspective effect. Three other arcades have been opened in London 

 since the erection of the Lowther Arcade. The first of them, Exeter 

 Arcade, running from Wellington Street to Catherine Street in the 

 Strand, erected in 1844 from the designs of Mr. Sidney Smirke, is very 

 short; is more enclosed than either Burlington Arcade or Lowther 

 Arcade ; has a vestibule at each end ; is glazed, so that the lights form 

 a continuous skylight, and has polychromic embellishment applied 

 both on the upper part of the walls (in ornaments and panels between 

 the windows over the shops) and on the cove of the ceiling. The 

 whole place has indeed more the appearance of a hall or gallery than of 

 a place of thoroughfare and business. The arcade in New Oxford 

 Street, opened in 1851, is short but of rather pretentious character. 

 Both of these have proved commercially unsuccessful, and neither is, 

 in fact, now employed for the purpose for which it was constructed. 

 The South-Eastern Arcade, at the entrance of the South-Eastern 

 Railway Station, London Bridge, is only remarkable for its unmitigated 

 architectural baldness and poverty. In Paris arcades have obtained 

 much greater popularity than in London. Among the Parisian 

 arcades, the Passage Colbert is oue of the most striking, both for its 

 extent and architectural display, towards which last its Rotunda 

 contributes hi no small degree. 



ARCH. The origin of that species of construction called an arch is 

 unascertained ; it cannot be stated with certainty either in what country 

 or at what epoch it was first used. There is good reason to think that, 

 though the arch form was certainly known to the Pelasgic inhabitants 

 of Greece, it was unknown to the Greeks at the time when they pro- 

 duced their most beautiful temples, in the fifth, fourth, and third 

 centuries before the Christian era. No structure answering to the 

 true character of an arch has been found in any part of those works, 

 though many occasions occur in which the application of the arch 

 would have been of great service, and would seem unlikely to have 

 been passed over by an intelligent and ingenious people like the Greeks 

 if they had been acquainted with the principle. The want of the arch 

 would necessarily lead them to contract the intercolumniation, or 

 spaces between the columns, and to the general and frequent adoption 

 of columns as the only mode of supporting a superstructure. But 

 though not appropriated at least for their sacred buildings by the 

 Greeks, it is now certain that the arch was known both to the 

 Egyptians and the Assyrians. There are brick arches at Thebes in 

 Egypt, which belong to a very remote epoch, and one long prior to the 

 Greek occupation of that country. Minutoli (' Reise zum Tempel des 

 Jupiter Ammon ') has given two specimens of Egyptian arches, one of 

 which is a false and the other a true arch. The first specimen is from 

 the remains t Abydos in Egypt (p. 245), where the roof has the appear- 

 ance of an arch, but is formed by three horizontal stones, of which that 

 which occupies the centre and lies over the other two is the largest ; 

 the three stones are cut under in such a way as to form a semicircle. 

 The true specimens are at Thebes (at least as early as B.C. 1490), on the 

 west side of the river (p. 260), near and behind the building which con- 

 tains the fragments of the enormous statue. They are circular arches, 

 and formed of four courses of bricks (see pi. 29), and on the walls there 

 are Egyptain paintings and hieroglyphics. (See also Belzoni's ' Plates," 

 No. 44, and his remarks on the brick arches of Thebes ; and also Sir 

 Gardner Wilkinson's ' Egypt and Thebes,' pp. 81 and 126 ; ' Manners 

 and Customs of the Egyptians,' vol. iii. ; and Colour, p. 297.) The stone 

 arches in the Nubian pyramids can hardly perhaps be adduced in proof 

 of the early use of the arch, as these edifices are probably not of very 

 high antiquity (see Cailliaud's ' Plates,' No. 43), though Mr. Hoskinn 

 (' Travels in Ethiopia ') attributes to the latest of them a date not more 

 recent than that of Cambyses. A stone arch of a date not later than 

 that of Psammeticus has been discovered at Saccara, and another in a 

 tomb near Gizeh. Mr. Layard and M. Place found both round and 

 pointed arches at Nimroud and at Khorsabad, the construction of 

 which shows that the ancient Assyrians were at a very early period 

 sufficiently acquainted with the constructive value of the arch to apply 

 it to a variety of important purposes. In the roofs of the tombs of Lycia, 

 of about the 5th century B.C., the pointed arch occurs. (Fellowes 1 

 ' Lycia ; ' and the works of Forbes and Spratt.) Etruria seems, from the 

 best evidence that can be obtained, to have been the first place in Europe 

 where the arch was employed ; and to the Etrurians may be assigned 

 the honour of its earliest applications, as far as our positive and undis- 

 puted information goes, in works of an important size and character, in 

 a pointed as well as in the circular form. The great sewer of Rome, 

 commonly called the Cloaca Maxima, is an arched construction, which 

 can hardly be referred to any period in the history of the city with so 

 much probability as to that to which it is assigned by uniform tradition, 

 namely, the age of the Tarquins. But though we may readily admit 

 this early date, we cannot say whether the architects were Roman or 

 Etrurian, though the latter would seem the more probable. 



The application of the arched structure is one of the most useful 

 mechanical contrivances ever discovered by man. By means of it, 

 small masses of burnt clay, and conveniently sized pieces of soft and 

 friable sandstone, are made more extensively useful for the economic 



