1839.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



18S 



Vo find their way to tlic young mind (if, indeed, they reach it at all), ratlier 

 as a relaxation of the graver business of education than as a part of it. 



Tlie illustrations of the meclianioal properties of matter and the laws of 

 force are drawn promiscuously and almost equally from art and natiu'o. It 

 is not by design that examples taken from these distinct sources thus inter- 

 mingle, but simply because they suggest themselres as readily from the one 

 source as the other — from nature as abundantly as from art. There is a 

 relation between art and nature — a relation amounting to more than a re- 

 semblance ; — a relation by which the eye of tlu^ practical man may bo guided 

 to that God who works with him in every operation of his skill, and 

 mechanical art elevated from a position which is sometimes luijuatly as- 

 .'•ignied to it among the elements of knowledge. It is from this relation 

 between the .Author of nature and thc^ being in whom the works of art 

 have their origin tliat arise those relations, inliiiitely remote, bnt distinct, 

 between tlie things themselves, of which llie evidence is eveiy where around 

 us. These are necessary relations : it is not that the works of art are 

 made by any pui'pose or intention in the resemblance of those of nature, or 

 that there is any imseen influence of nature itself upon art; the primary 

 relation is in the causes whence these severally proceed. Thus it is possi- 

 ble, that in the infinities of nature, every thing in art may find its type ; this 

 is not. however, necessarily the case, since the causes are infinitely re- 

 moved, since, moreover, in their operation, these causes are independent, 

 and since nature oper.ates upon materials which are not within tlie resources 

 of art. How full of pride is the thought, that in evei-y exercise of human 

 fikill, in each ingenious adaptation, and in each complicated contrivance 

 and combination of art. tliere is included the exercise of a faculty which is 

 akin to the wisdom manifested in creation ! And how full of humility is 

 the comparison wliicli, placing the most ingenious and the most perfect of 

 tlie efforts of human skill by the side of one of the simplest of the works of 

 nature, shows us but one or two rude steps of approach to it. 



The arrangement of the work will perhaps be better understood by 

 leaving it in the author's own words, so that we have selected for our 

 readers the following detail of it :— 



Matter is composed of elements, which are inappreciably and infinitely 

 minute ; and yet it is witliin the infinitely minute spaces wliich separate 

 these elements that the greater number of the forces known to us have 

 their only sensible action. These, including compressibility, extensibility, 

 elasticity, strength, capillary attraction and adhesion, receive their illustra- 

 tion in the first three chapters of the following work. The fourth takes up 

 the Science of Equilibrium, or Statics ; applies in numerous examples the 

 fimdamental principles of that science, the parallelogram offerees, and the 

 equality of moments ; then passes to ihe question of stability, and to the 

 conditions of the resistance of a surface ; traces the operation of each of 

 the mechanical powers under the influence of friction ; and embraces the 

 question of the stability of edifices, piers, walls, arches, and domes. 



The filth chapter enters upon the Science of Dynamics. Numerous 

 familiar illustrations establish the permanence of the force wliich accompa- 

 nies motion ; show how it may be measured ; where in a moving body it 

 may be supposed to be collected ; exhibit the important mechanical pro- 

 perties of the centres of spontaneous rotation, percussion, and gyration j 

 the nature of centrifugal force ; and the properties of the principal axes of 

 a body's rotation ; the accumulation and destntction of motion in a moving 

 body, and the laws of gravitation. 



The last chapter of the work' opens with a series of illustrations, the 

 object of wliich is to make intelligible, under its most general form, the 

 principle of virtual velocities, and to protect practical men against the 

 errors into which, in the application of this universal principle of me- 

 chanics, they are peculiarly liable to fall : it terminates with .various illus- 

 trations of "those general principles which govern the reception, transmis- 

 sion, and application of power by machinery, fhe measure of dynamical 

 action, and the numerical cfKciencies of different agents — principles which 

 receive their final application in an estimate of the dynamical action on the 

 moving and working points of a steam engine. 



The Appendix to the work contains a detailed account of the experi- 

 ments of Messrs. Hodgkinson and Fairbairn upon the mechanical properties 

 of hot and cold blast iron : and an extensive series of tables referred to in 

 the body of the work, and including, 1. Tables of the strength of materials ; 

 '2. Tables of the weights of cubic feet of different kinds of materials • 

 3. Tables of the thrusts of semi-circular arches under various circum- 

 stances of loading, and of the positions of their points of rupture ; 4. Ta- 

 bles of eo-efticients of friction, and of limiting angles of resistance, com- 

 piled and calculated from the recent experiments of M. Morin. The results 

 of these admirable experiments, made at the expense of the French 

 government, are here, for the first time, published in this country. 



A Dictionary of Arts, Manvfactures, andMines. By Andrew Uhe, M.D. 

 London. Longman and Co. 



We have now come to a final notice of this work, and we cannot 

 dismiss it without presenting to our readers a few more extracts. The 

 following is from the article on slate, and gives a brief sketch of the 

 localities in which that material is found : — 



Clay -slate. ^-"VU-is substance is closely connected with mica; so that 

 iminterrupted transitions may be found between these two rocks in many 



mountain chains. It is a simple schistose mass, of a bluish-gray or grayish- 

 black coloiu-, of various shades, and a sliining, somewhat pearly internal 

 lustre on the faces, but of a dead colour in the cross fracture. 



Clay-slate is extensively distributed in Great Britain. It skiit^ ,th« 

 Highlands of .Scotland, from Lochlomond by Callender, Comrie, and 

 Dunkeld; resting on, and gradually passuig into mica-slate throughout 

 the whole of that territoiy. Roofing-slate occurs, on the western side of 

 England, in the comities of Cornwall and Devon; in various parts of 

 North Wales and Anglesea; in the north-east parts of Yorkshire, near 

 Ingleton, and in Swaledale ; as also in the counties of Cumberland and 

 Westmoreland. It is likewise met ^vith in the county of Wicklow and. 

 other mountainous districts of Ireland. 



All the best lieds of roolihg-sUte improve in quality as tliey lie deeper 

 under the surface ; near to which, indeed, they have little value. 



A good roofing-slate should split readily into thin even laminoe ; it 

 should not be absorbent of water either on its face or endwise, a pro- 

 perty evinced by its not increasing perceptibly in weight after immersion 

 in water ; and it shoidd be sound, compact, and not apt to disintegrate in 

 the air. The slate raised at Eisdale, on the west coast of Argjdlshire, is 

 very durable. 



Cteaoing and dressing of the slates. — The splitter begins by dividing tha 

 block, cut lengthwise, to a proper size, which he rests on end,- and steadies 

 between liis knees. He uses a mallet and a chisel, which he introduces 

 into the stone in a direction parallel to the folia. By this means hp 

 reduces it into several manageable pieces, and he gives to each the r-equi- 

 site length, by cutting cross grooves on the flat face, and then striking tlie 

 slab with the chisel. It is afterwards split into tliinuer sections, by finer 

 cliisels dexterously applied to the edges. The slate is then di'essed to the. 

 proper shape, by being laid on a block of wood, and having its projecting, 

 parts at the ends and sides cut ofl' with a species of hatchet or chopping- 

 knife. It deseiTes to be noticed, that blocks of slate may lose their pro- 

 perty of divisibility into thin lamina?. This happens ii'om long exposiu'q to 

 the air, after they have been quarried. The workmen say, then, that they 

 have lost their waters. For tliis reason, the number of splitters ought to 

 be always proportioned to the number of block-hewers. Frost >:endev3 the 

 blocks more fissile ; but a supervening thaw renders them quite refractory. 

 A new frost restores the faculty of splitting, though not to the same degree ; 

 and the workmen therefore avail themselves of it without delay. A suc- 

 cession of frosts and thaws renders the quarried blocks quite intractable. 



This account is, however,- rather meagre, as it totally omits one of 

 the great districts, that of Furness, in Lancashire, wliicii supplies slate 

 of excellent quality, and much used in that neighbourhood. There is 

 no distinction made between the several varieties, and the manner in 

 which the locality is determined by the colouring of the slate, the 

 slates of Cornwall and Westmoreland differing totally in respect to 

 colour. The application of slate also as a paving material, and its 

 applicability in solemn decoration, as for tombstones, library chimnej'- 

 pieces, slabs, &c., are not alluded to. The ensuing account of the 

 manufacture of stained glass is rather more chemical than practical ; — 



St.vined Gl.\ss.— When certain metallic oxides or chlorides, gi'ound up 

 with proper fluxes, are painted upon glass, their colours fuse into its stuv 

 face at a moderate heat, and malce durable pictures, which are frequently 

 employed in ornamenting the windows of churches as well as ot other 

 public and private buildings. The colours of stained glass are all trans- 

 parent, and are therefore to be viewed only by transmitted light. Many 

 metallic pigments, which afford a fine effect when applied cold on canvas 

 pr paper, are so changed by yitieous fusion as to be quite inapplicable to 

 painting in stained glass. 



The glass proper for receiving these vitrifying pigments, should be 

 colourless, uniform, and difficult of fusion ; for which reason crown glass, 

 made witli little alkali, or with kelp, is preferred. When the design is 

 too large to be contained on a single pane, several are fitted together, and 

 fixed in a bed of soft cement while painting, and then taken asunder to be 

 separately subjected to the fire. In ananging the glass pieces, care must 

 be taken to distribute the joinings so that the lead fiame-work may 

 interfere as little as possible with the effect. 



A design must be drawn upon paper, and placed beneath the plate of 

 glass ; though the artist cannot regulate his tints directly by his pallet, 

 hut by specimens of the colours producible from his pallet pigments 

 after they are fired. The upper side of the glass beuig sponged 

 over with gum-water, affords, when dry, a surface proper for receiving the 

 coloui-s, without the risk of theii- running irregularly, as they would be 

 apt to do, on the slippery glass. The artist first draws on the plate w-ith a 

 fine pencil, all the traces which mark the gi'eat outlines and shades of the 

 figures. Tills is usually done in black, or, at least, some strong colour, 

 such as browTi, blue, green, or red. In laying on these, the painter is 

 guided by the same principles as the engiavei-, when he produces the effect 

 of light and shade by dots, lines, or hatches ; and he employs that colour 

 to produce the shades, which will harmonize best with the colour which is 

 to be afterwards apphed ; but for the deeper shades, black is in general 

 used. When this is finished, the whole pictm'e will be represented in 

 lines or hatches similar to an engraving finished up to the highest efffCt 

 possible; and aftciwards, when it is dry, the vitrifying colours are laid on 

 by means of larger hair pencils ; their selection being regulated by the 

 bm'nt specimen tints. When he finds it necessary to lay two colours 

 adjoining, which are apt to run together in the kiln, he must apply une.of 



