SKEW-15RIDGE. 



SKIN", DISEASES OK. 



b* that UM joinU of the Yousaoin, whether of brick or stone, should 

 be rectangular with the abutment, instead of being parallel with the 

 face of we arch. Thus the couraes, instead of taking the direction 

 shown in t-j. 3, were laid in the manner indicated iu Jig. 4. One of 





the first bridges built on this plan, the Finlay bridge, near Naas, 

 crossed the canal at an angle of only 39; the oblique span being 25 

 feet, and the height of the arch 5 feet 6 inches. Mr. Chapman observes 

 that the lines on which the beds of the voussoirs lie are obviously 

 spiral lines, and to this circumstance may be attributed much of the 

 singular appearance of oblique arches. The Finlay bridge stood well, 

 but the ingenious designer did not think it prudent in any other case 

 to attempt so great a degree of obliquity, although he built several 

 other bridges on the same principle, over the Grand Canal in Ireland, 

 and over some wide drains in the East Riding of Yorkshire. lie 

 recommends carrying up the masonry as equally as possible from each 

 abutment, in order to avoid unequal strains on the centering. 



On the Liverpool and Manchester railway, out of rather more than 

 sixty bridges, about one-fourth were built on the skew ; one, built of 

 stone, conducting the turnpike-road across the line at Rainhill, being 

 at an angle of only 34, by which the width of span is increased from 

 80 feet, the width of the railway from wall to wall, to 54 feet, the width 

 on the oblique face of the arch. Skew-bridges have since become very 

 common, and some have been erected of even greater obliquity. That 

 at Box-moor, on the London and North- Western railway, was for long 

 unrivalled for obliquity by any other brick arch. Its angle ia 32 , 

 the square span 21 feet, and the oblique span 39 feet. There are also 

 brick arches of great obliquity on the Greenwich and Blackwall rail- 

 ways, but with their precise angles we are unacquainted ; on the Paris 

 and Rouen railway there is a skew-bridge of brickwork with stone 

 bond courses of 28' of obliquity. 



From Mr. Buck's treatise on oblique bridges, it appears that the 

 difficulty of building skew-bridges increases with the obliquity of the 

 angle from 90 to 45, which ia supposed to be the most hazardous 

 angle for a semicircular arch ; but that beyond that point, instead of 

 increasing, it rather diminishes to about 25", which appears to be about 

 the natural limit for a semi-cylindrical arch. Mr. Buck, whose ex- 

 perience renders his opinion highly valuable, considers that oblique 

 arches of the elliptical form should not be attempted, as they are 

 deficient in stability, more difficult to execute, and more expensive 

 than semicircular or segment.il arches. 



The construction of skew-bridges of iron or timber is comparatively 

 simple, the ribs or girders of which such bridges are composed being 

 of the usual construction, laid parallel with each other, but the end of 

 each being in advance of that next preceding it. fig. 5 represents the 



Fig. 5. 



ground-plan of such a bridge, the dotted lines indicating the situation 

 of the ribs upon which the platform is supported The extraordinary 

 iron bridge by which the Manchester and Birmingham railway is con- 

 ducted over Fairfield-otreet, Manchester, at an angle of only 244, is a 

 fine example of this kind of skew-bridge. It consists of six ribs, of 

 rather more than 128 feet span, although the width of the street is 

 only 48 feet, resting upon very massive abutment* of masonry. The 

 total weight of iron in this bridge, which is considered to be one of 

 the finest iron arches ever built, is 540 tons. It was erected from the 

 design of Mr. Buck, who has constructed several other oblique bridges 

 of great size and very acute angles. Timber bridges, formed of trussed 

 ribs or girders, are built on the same principle. One of very great 

 olili.piity, on the Sechill railway, is represented in the second series of 

 Brees's ' Railway Practice.' A somewhat similar mode of constructing 

 skew-bridges in brickwork was introduced by Mr. Qibbs on the Croydon 



railway. The Jolly Sailor bridge, which crosses over this line near 

 Norwood, consisted originally of four separate ribs of brickwork, 

 each forming an elliptical arch of 00 feet span, with a versed sine of 

 12 fret inches, supporting a flat viaduct of Yorkshire flagstones. 

 Each of these ribs, which were three feet wide on the transverse face, 

 was built square, so that the brickwork was of the simplest kind; 

 but by making the respective abutment* project beyond each otlur 

 according to the oblique direction of the railway, the ribs, taken 

 collectively formed a skew-arch. In a bridge erected by Mr. Wood- 

 house on the line of the Midland Counties railway, the same principle 

 is adopted, but the ribs are placed close together, so that no platform 

 of flagstones is required. 



SKIN, DISEASES OF. Most of the diseases of the skin are 

 described in this work under their particular names. In this article we 

 shall supply an arrangement of them, and a description of those which 

 are not described under special heads. The following arrangement is 

 that adopted by Rayer in his work on diseases of the skin : 



Class I. INFLAMMATION OF THE SKIN. 



Order 1. Exanthematoia. Rubeola, Roseola, Scarlatina, Urticaria, 

 Erythema, Erysipelas. 



Order 2. BuUuvu. Vesication, Ampulla;, Pemphigus, Rupia, Zona. 



Order 3. Veticntmu. Herpes, Psora, Eczema, Miliaria. 



Order 4. Putiuluia. Varicella, Variola, Vaccinia, Vaccinelb 

 thyma, Cuperoea or Acne, Mentogra, Impetigo, Tinea, Artificial 

 pustules. 



Order 5. Furunruloui. Uordeolum, Furuncle, Anthrax. 



Order 6. Papvlotu. Strophulus, Lichen, Prurigo. 



Order 7. TubercuUna Lupus, Cancer, Elephantiasis of the Greeks. 



Order 8. Squamout. Lepra, Psoriasis, Pityriasis [SCURF]. 



Order 9. Linear. Fissures. 



Order 10. Oangrenoiu. Malign pustules, Carbuncle of plague. 



Order 11. Multiform. Burns, Frost-bite, Syphilitic eruptions. 



Class II. CUTANEOUS AND SUBCUTANEOUS CONGESTIONS, AND 



' HAEMORRHAGES. 



Cyanosis, Vibices, Petechiae, Purpura Hiemorrhagica, Ecchymosis, 

 Dermatorrhagia. 



Class III. NERVOUS DISEASES OF THE SKIN. 



Exaltation, Diminution, Abolition of the sensibility of the skin, 

 without appreciable alteration in the texture of this membrane. 



Class IV. ALTERATIONS IN THE COLOUR OF THE SKIN. 



Order 1. Decoloration. Leucopathia, partial, general ; Chlorosis. 

 Order 2. Accidental Colorationt. Ephelis, Lentigo, Chloosma, Mela- 

 dennis, Icterus, Njevus maculosus, Argentism. 



Class V. MORBID SECKKTIONS. 

 Ephidrosis, Acne, Folliculous Tumours. 



Class VI. DEFECTS OF CONFORMATION AND TEXTURE. 



Distention of the Skin, Cicatrices, Vegetations, Nsevus hoematodes, 

 Subcutaneous vascular tumours, warts, pearly granulations ; Corns, 

 Ichthyosis, Horny appendages. 



Diseases of the skin are very numerous and prevalent, but in the 

 case of the majority which occur they arise from the neglect of some 

 of the conditions necessary for the health of the skin. These con- 

 ditions in general are, good nutritious food, which should be properly 

 digested; a due amount of warm clothing, especially during changeable 

 and cold weather ; constant and regular exercise, so as to keep the 

 skin as an excretory organ in perfect order; and daily ablution of every 

 part of the body, without which and the occasional use of soap it is 

 vain to expect to be free from many forms of skin disease. 



The following are the diseases which appear to demand further 

 notice : 



Eczema, Heat-eruption, is an inflammation of the skin, characterised 

 at the outset by small non-contagious vesicles, the fluid of which is 

 finally reabsorbed ; by superficial excoriations, attended by a serous 

 discharge, or by a squamous condition of the skin. This disease may 

 be confined to one particular part of the body, or it may attack the 

 whole surface. It may arise from a local cause, as from the direct 

 rays of the sun, or from some general disturbance of the system. The 

 vesicles may be only few, and the surrounding skin only slightly inflamed 

 and confined to a very limited surface, or the vesicles may be nume- 

 rous, the excoriations painful, the surface attacked extensive, and the 

 tendency to inflammatory action in the skin so strong as to produce 

 pustules instead of vesicles. Such arc the characters of the three forms 

 of eczema usually described by writers on diseases of the skin. . 

 toltirit, B. rubritm, K. impetiginoides. Eczema is more likely to be con- 

 founded with itch than any other disease, from which it may be dis- 

 tinguished by its non-contagiousness and the very different parts of 

 the tegumentary system which it oocu]>i 



There is a form of eczema which comes on from the exhibition of 

 mercury and the external application of other medicines, and which 

 frequently arises from the carelessness of the person attacked, which is 

 called E. mercuriale. 



