Class XXIV.] COMPONENTS, PROPERTIES, &c., OF GLASS EMPLOYED.

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rest of tine establishment, stores, &c., are kept at thedepot in tihe island of Tyree. The light of the Skerry-vore is revolving, and is produced by the revolution ofeight aiiuiular lenses around a ceutral lamp, and belongsto the first order of dioptric lights in the system ofFresnel, and may be seen from a vessel’s deck at adistance <of 18 miles. An arrangement of apparatus ofconsiderable importance has been suggested by Mr. Thomas Stevenson. , whereby true lenticular action may be extendedby the adtoptiou of total reflection for that end. By thisarrangennent, combined with the use of spherical mirrors,he has be<cn enabled to use all the light of a lamp, and hehas therefore termed it a holophotal system. Much hasbeen dome of late by the English , the Scotch, and theIrish Boairds for the improvement of the lighthousesystem; but the interests of commerce and of humanityrequire thiat much more should be done,—as the funds setapart for this object will permit,—in order to afford stillgreater security to vessels approaching our coasts; andwe trust tchat the British manufacturers will not be slowin availimg themselves of the opportunity of supplying amaterial mf the very best quality for this important object.

In a slketch of this nature, it is for obvious reasonsextremehv desirable to avoid anything like a comparisonbetween ’ the products of different countries or differentindividuails; but it manifestly comes within the scope ofour duty to give a brief account of the rise and presentposition o>f the principal establishments which have con-tributed ulieir productions to the Exhibition ; and to takea gencrall view of the state of the manufacture in thosecountries., which have, at expense and inconvenience tothemselv<es, intrusted their property to our care, andconfided in our impartiality and justice in determining tothe best cnf our ability their respective merits.

In the progress of this undertaking, we have felt anincreasing* sense of the importance of the subject, and ofthe responsibility arising out of the task. We have feltthat the contributors might reasonably desire a moredetailed (description of the products which they have con-tributed tto the Exhibition, and of the art to which theyhave uppdied their intellect, their resources, and theiriudustry. But our limits are necessarily restricted withinnarrow bounds, and we fear that we have already tres-passed ujpon the Commissioners and the public, furtherthan the object, intended in calling for Reports from theJuries, fiully justifies. But we must plead in our excusethe interest and importance of the subject—an interestwhich w<e have felt growing upon us as we proceeded;and thouigh we are aware that the subject has frequentlybeen well! and ably treated, yet we trust that in pointingout some novelties and improvements in the art, to whichrecent practice has given rise, we shall obtain forgivenessfor exceeding in some small degree the limits assigned tous. In tthe remarks which we feel ourselves called uponto make, it has been our most anxious desire not to woundthe feelimgs of any exhibitor, still less to do him an injuryin his trade by any observation of ours, applying to hiswork. We have endeavoured to confine ourselves togeneral ^principles, not to point out defects; but to leaveit to the exhibitor to judge for himself, whether our prin-ciples are correct, and whether he has acted in accordancewith therm; and if not, to amend his practice, and entitlehimself tco commendation on some future occasion.

There are, however, points at issue to which it is ex-tremely important to call the most serious attention ofthe maniufacturer. A difference of opinion prevails as tothe actuail composition of glass, and this must be regardedas a difference of principle. A practical difference pre-vails, particularly in cast plate-glass, as to the finishingand poliishing. By finishing is meant the process ofrubbing away the roughness or marks occasionally lefton the suirface after grinding, which will always be per-ceptible iif they are not carefully removed before the glassis polislned ; and will consequently deteriorate its quality.

Lastly , the question of price.

With respect to the first question—the composition ofthe metad—upon this must depend the merit of the glass,and cons<equeut!y its value. The combination of as muchbrilliancy of refraction with as perfect purity of colour ascan be obtained is the object desired.

By some manufacturers, purity of colour is sacrificedto brilliancy of refraction; by others, the reverse is thecase. The real object, the juste milieu , can only beattained by a judicious selection and apportionment ofthe materials employed; and this can only be the resultof careful experiments, and the study of the effect ofvarious chemical combinations. The expulsion or reten-tion of the alkalies, the metallic oxide used, the amountof heat employed, and the annealing process, are veryimportant considerations in determining this question.

in some descriptions of glass the defect of colour isless apparent than in others. In mirrors a greenish hue,or a dull, heavy appearance in the glass, cannot fail ofimparting to the object reflected a portion of its colourand tone; and in proportion to the extent of the defect,deteriorating the merit of the glass. The French and theBelgians have paid great attention to this circumstance ;and judging from the specimens of the Cirey and St. Gobain glass in the Exhibition, and of the Belgian glass,which we have likewise seen in the hands of persons whohad not the opportunity of exhibiting them, we shouldsay, that if these glasses maintain their present appear-auce, and do not exude moisture, a very great advancehas been made in the art, and a very perfect article ofmanufacture attained.

In England, the long-continued pressure of taxationexercised its influence over this species of glass, which,in consequence of its high price, was not in very greatdemand until the removal of the evil enabled the manu-facturer to reduce his price, and improve the quality ofhis glass. Glass for glazing windows has been employed,in this country, to a far greater extent than silvered glassfor mirrors; and the defect in colour is not so muchperceived in the transparent glass, as in the latter. Weare likewise told that, since the diminution in price, whichtook place on the reduction of the duties, the demand forboth silvered and transparent plate-glass has increased toso great a degree, that hands cannot be found to supplythe wants of the public; and that the consequence hasbeen a less careful fabrication of the material, or rather afabrication of an inferior article, at the lowest price pos-sible. It has been stated, that the more perfect manu-facture of the French and Belgian artists will not standthe test of time, and that deterioration will occur, bothin colour and structure, by the decomposition of thealkalies used in the manufacture.

We reply, that we are informed the practice of theCirey and St. Gobain manufacturers is, to keep a verylarge quantity of their glass in store, sometimes for manyyears together, and that they have never experienceddeterioration, and consequently do not fear its occurrencethrough lapse of time; and that, though we may admitit may be both right and politic to supply the public witha low-priced article of inferior quality, we do not believethose manufacturers are consulting their own interest,who fabricate an important article in an inferior manner,and who exhibit products, calculated to attract the wealthyand the fastidious by the qualities of magnitude and beauty,but which, on inspection, are found liable to be chargedwith the defect of colour, of stria', of globules, of undu-lations, &c. We believe that success in trade, as well asthe honour of excelling in manufacture, requires grada-tions in fabrication, suitable to the means and tastes ofthe different classes of purchasers; hut that each grada-tion should be as good of its kind, as the nature of itsprocess will admit of its being made.

With respect to the third question, that of price, it is ofcourse a most important question; and it is a most difficultone to answer. The Commissioners had the questionunder their consideration for a considerable time, and atlast wisely detennined not to meddle with it. It does notdepend upon arbitrary regulation, but upon circumstanceswhich are necessarily fluctuating. Capital, taxation, sup-ply and demand, fashion, all more or less affect prices,and prevent them from being the real indicators of theintrinsic value <of an article exposed for sale.

Having ventured to make these general observations,it only remains for us to state the principle upon whichthe award of Medals has been made, and the groundsupon which the Jury has decided in favour of the suc-

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