the new-york EXHIBITION ILLUSTRATED.

span to the opposite pier-head. The floor beams are merely for the purpose ofcarrying the rail, and, it is stated by the inventor, are not adapted to performingany function of support to the bridge.

Fink's Bridge .—The model of an iron bridge by Albert Fink, of Baltimore,>s also a cast-iron trussed girder, similar in principle, but in some respects superiorto that at Harper’s Ferry. Its construction is shown in the preceding drawing.

Long's Bridge .—The model of an iron bridge invented and patented by ColonelS- H. Long, of the U. S Top. Engs., is exhibited by M. M. White, agent, New-port. It is a variety of the ordinary lattice bridge, which has been a number ofyears before the public under the name of Rider’s Bridge. It is a straight truss^ith cast-iron upper chords, and vertical ties, and wrought-iron diagonals, andlower chords, counterbraced by keys or wedges at the tipper ends of the ties.Owing to the simplicity and similarity of the parts, it is cheaply and readilyframed, and for small spans is an economical bridge. Butin cases where the mag-nitude of the undertaking requires the rejection of every pound of useless mate-tial, and the employment of the remainder to its fullest extent, an examination ofthe governing principles of the arch will soon lead to a consideration of the differ-ence of the strains at the crown and the heels, and a disposition of the materialto meet them, unlike the uniformity which prevails in this plan.

tl Uncle Sam Bridge ,” invented by Hammond Howe, of Cincinnati. It is statedLy the inventor, that this model of a horizontal truss bridge which may be constructed°f wood or iron, is 16 feet long, weighs 63 pounds, and can carry 8448 pounds; it re-presents a bridge 480 feet long, containing 135,000 feet, board measure, of timberAveraging six inches square, and 47 tons of iron, and which will be capable of carry-fog 10,800 tons. Its distinguishing characteristics are straight lower chords, andarched upper ones, springing from points sufficiently high to clear the roadway,and with a rise nearly sufficient to double the depth of the truss at the centre.The immense span represented by the model, and the employment of smalltimber, produces an effect of complexity of parts which the structure would notPossess. The ties, braces, and counterbraces, are well arranged in sets graduallylessening in lengths towards the abutments, and properly disposing the timbersvertically at the piers, and at their most acute angles near the centre. It is prob-ably overloaded in the middle, and the secondary chord to the upper arch, if thebraces are well bolted, is of no utility. The butting blocks at the heels of thebraces are superior to the ordinary joints.

PENNSYLVANIA MINERALS.

Miking is a most fascinating pursuit, involving the pleasure of a hazardous ad-venture and the excitement of successful play. Its profits are sometimes sofr bulous, that its losses are overlooked, and men are always ready to venture even^Ith the smallest evidence upon its large and certain expenses. Although Amer-fra, from its discovery until this day, has furnished the great bulk of the preciousPetals, mining, as an art, or as a science, has never been well understood here,n °r systematically followed—and especially in the United States. Gold beingfound for the most part on the surface, in the alluvial sands, is extracted by ther >idest means and the most unskilful operators—the process being unworthy of then ame of mining. The few deep mines in Virginia and the Carolinas, where thegold-bearing rocks are wrought, scarcely form an exception to this remark. TheWes of silver, and those of the less valuable metals, are, however, to be procuredonl y by deep mining, and the resources of the United States in this direction haveyet to be developed. The galena (ore of lead) of Missouri and the adjacentlegions, has been hitherto dug from beds of clay at an inconsiderable depth. Thereis no regular lode or vein, and the process of procuring it is even less like mining,tiian the washing of auriferous sands. The native copper of Lake Superior, has noa nalogy in the previous history of mineral explorations; and while its returnsbave been in several cases most encouraging, and remunerative to the share-ciders, we are still too inexperienced in this new mode of copper-mining to enable113 to speak with certainty of its future success.

We are lead to speak of thiB subject by the exhibition of the ores of leadfrom the ‘Wheatley Mines in Pennsylvania, accompanied by diagrams of the mines,of the machinery used in working them, and specimens of the several products.Pennsylvania has immense wealth in coal and iron, as all the world knows; buther resources in copper, lead, and zinc, are now only beginning to be developed.The collection of Pennsylvania coals and irons, made under the supervision of Dr.O. M. Wetherell, will be the subject of a future notice.

The mineral region where the "Wheatley Mines are situated, is in Montgomeryand Chester Counties, and occupies a belt of country from six to seven miles long,ranging across the Schuylkill River, near the Perkiomen and Pickering Creeks, ina general east and west direction, and along the boundary of the so-called primaryand secondary rocks. The existence of some of the metallic veins of this regionhas been long known, but it is only lately that a systematic exploration of theircontents has been undertaken by Mr. Charles M. Wheatley. Under) his judiciousmanagement, the chief lode of argentiferous galena has been proved to a depth ofover two hundred feet, and a monthly return of about one hundred tons ofsilver-lead-ore obtained. The mineralogist, and the lover of beautiful nat-ural objects, will see with equal pleasure and surprise the superb crystallisation ofmetallic salts from these mines, now exhibited in the Mineralogical Department.They embrace the carbonate of lead, sulphate of lead, (anglesite of the mineral-ogists), phosphates of lead, green, brown, and yellow; molybdate and molybdo-chromate of lead, splendid red crystals; arseniate of lead, chromate of lead, galena,bars of silver obtained from the galena, and various other products less attractive tothe uninstructed eye. We speak understandingly and without exaggeration, whenwe say that the sulphates and molybdo-chromates of lead in Mr. Wheatley’s col-lection, are the most magnificent metallic salts ever obtained in lfead mining, andunequalled by any thing we have seen in the cabinets of Europe.* These attractive

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HIGH-PRESSURE 24-INOH PUMPING ENGINE IN U8K AT THE WHEATLEY MINE.

* [ Selecting the Wheatley Lode as presenting perhaps the greatest diversity ofspecies, and as that which has received the closest study, we find the mineralogyof these veins represented by the following large and interesting catalogue ofspecies:

Sulphate of Lead Crystallised,Carbonate of Lead “

Phosphate of Lead “

Arseniate of Lead “

Molybdate of Lead “Chromomolybdate of Lead,Arseniophosphate of Lead,

Sulphuret of Lead,

Antimonial Sulphuret of Lead andSilver,

Sulphuret of Zinc,

Carbonate of Zinc,

Silicate of Zinc,

Sulphuret of Copper,

Green Malachite,

Blue Malachite,

Black Oxyd of Copper,Native Copper,

Oxyd of Manganese,Native Sulphur,

Native Silver,

Quartz crystallised,Cellular Quartz,

Oxyd of Iron with Silver,Brown Hematite,

Brown Spar,

Sulphate Barytes,

Iron Pyrites.]