A large audience assembled in Steinway Hall, 17th February, to hear the last lecture of the course before the American Institute. Ths lecturer, after a few introductory remarks, said : Engineering is peculiarly the exponent of modern development. Its definition is " the acquisition of that species of knowledge whereby the great sources of power in nature are converted, adapted, and applied for the use and convenience of man," which covers the civil and military engineer, the architect and mechanician, the closet theorist, and the practical workman. The subject covers the locomotive and its railway; the steam engine and its application ; the metals and their manipulation ; the workshops and their great tools; modern ordnance and armor ; naval construction, telegraphy, bridges, canals, water supplies, harbors, etc.; and has been char-acteriz d by the various applications of steam, the product and manipulation of metals and telegraphy. Among the most important of the discoveries and appliances on modern engineering is the locomotive. It was invented at the beginning of this century, but was not successfully used until 1839, since which time it has increased from four to forty tuns in weight, and from fourteen to sixty miles per hour in spaed. Then grades of fifty feet per mile were the maximum, now those of 440 feet at Mont Cenis and 528 on the Baltimore and Ohio, have been used. Forty years ago Horatio Allen had to mount the foot-board oi the first locomotive himself, now 15,000 are daily whirling over 40,000 miles of railways in this country alone. To-day locomotives are passing over the summits of the Rocky Mountains and Sierra Nevada, and before the year closes will go from ocean to ocean. ,From the days of Noah until those of the locomotive, civilized population was confined to the water lines. This one engine has spread an avalanche of peoples upon onr fertile interior, who ' now form more than one half of our population and sources of prosperity. The Brie Canal, originally built for vessels of 00 tuns, has just been enlarged for those of 250 tuns, and its increasing traffic already demands an enlargement for vessels of 1,000 tuns. Of the traffic of the great West it now carries more than all of the great trunk lines of railway between the St. Lawrence and the Potomac. One canal boat carries more tannage than a freight train, and the Erie Canal brings daily to tide water more than five times as much tunnage as tho New York Central. Its tunnage exceeds that of all the foreign commerce of this city. The materials used in its construction exceed in quantity those required for the 2,000 miles of the Pacific Railway. The Croton Aqueduct exceeds in engineering merit any work of its kind in the world. The American examples of bridges embrace those of every material and forai, and many of huge dimensions. The Niagara and Cincinnati wire suspension, by Roebling ; the Havre de Grace of wood, by Parker ; the Schuylkill bridge of cast iron arches, by Kneass; and the Victoria iron girder by Stephen-son, are among the most noted. In submarine works are the piera of the Potomac and Croton Aqueducts, of the Havre de Grace and Harlem Bridges, and the founding of the United States Graving Dock, at Brooklyn. The Aqueducts and Graving Dock were founded by means of coffer dams, the Havre de Grace Bridge by means of iron caissons, and the piers of the Harlem Bridge are composed of large cast-iron columns or hollow piles, driven by the new-discoverod pneumatic process. A mass of metal of a tun weight was unknown before the Christian era. Now those in cast iron up to 150 tuns, in wrought iron to forty tuns, and in steel or bronze to twenty-five tuns, are cast in any desired form, and turned or bored with the most perfect accuracy. Two years ago I saw the largest lathe in England, which swings twenty-two feet, and will take in a shaft forty-five feet long. Six months ago I saw one in this country which swings thirty feet, and will take in a shaft of fifty feet. There are planers which will plane iron fifty feet in length ; others of eighteen feet in width ; others fourteen feet in hight, taking off metal shavings of two and a half inches in width and a quarter thick. Not long since I witnessed the penetration of a wrought-iron shield of fifteen inches thickness by an elongated cannon shot of twelve inches diameter. The largest European gun is of steel, by Krupp, fourteen inches bore, and will throw a ball of 1,000 pounds, but has never bsen fired. The next largest European gun, is an Armstrong rifle, which throws a shell of 610 pounds. The 12-inch American Rodman rifle throws an elongated shot of 630 pounds, and the 20-inch smooth-bore, a spherical shot of 1,072 pounds. The " Swamp Angel" is a Parrott rifle, eight inches bore, and threw shot of 150 pounds a distance of five and a half miles into Charleston. Its ancient rival, " Mons. Meg," is twenty inches bore, and threw stone balls of eighteen and a half inches in diameter, but notwithstanding its quaint legend, its range did not exceed a. mile and a half. It is said that telegraphy may be read by each of the five senses, namely, sight, sound, feeling, taste, and even smelling. The method of signaling through the Atlantic Cable is exactly the reverse of that upon the land lines, and is done by alternate currents of positive or negative electricity, but ten per cent of which is allowed to cross the ocean ; and, therefore, an almost microscopic receiving instrument is used. Last autumn General Reynolds sent a message ninety-two miles across Lake Superior by means of the heliotrope (or mirror) without the aid of either wire or cable. The works of the ancients are often referred to as excelling, in magnitude, accuracy of workmanship, and beauty of design those of modern times. This view is in part at least quite erroneous. Their works were generally for useless purposes, although there are many exceptions, such as their canals, water works, military roads and bridges, which show that they were occasionally called upon for works of utility. The stones in the temple of Baalbec are the largest save one of any building in the world. They range from 1,200 to 1,275 tuns. The one at St. Petersburg is one-fifth larger. The monoliths of _Egypt are from 200 to 300 tuns, and a few of 700 tuns. The obelisk of Luxor, now in ! Paris, weighs 250 tuns. The " goodly stones " of the temple at Jerusalem weighed 350 tuns each. The speaker then described, from the most trustworthy sources, the probable method of constructing the great Pyramid of Gizeh, including the method of quarrying, transporting, and laying the stone, and stated that, instead of scaffolding, a mound of earth and an inclined causeway were used, and when the structure was completed the earth was removed. This pyramid contained ? 6,500,000 tuns of stone, and the embankments required 50,000,-000 tuns of earth. All of the masonry of the Erie Canal amounts to but one-third of this, and all of the earth moved for the Pacific Railway amounts to but that used instead of scaffolding for this pyramid. It required the labor of 500,000 men for thirty years, and cost $5,000,000,000. A modern en-.' gineer would construct such a work for $100,000,000, and use a tithe of thg men. The Coliseum of Rome was of but one-third of the size of the London Exhibition building, and but one-sixth of tho Paris building. The tunnage of the Ark was 12,000 ; of the show ships built by Ptolemy somewhat less, and of the Great Eastern, 22,500 tuns. Some of the modern men-1 of-war have nearly 9,000 tuns displacement, and our passenger i ships 3,000 to 5,000 tuns. The largest steam engines in the world were those used in draining the Haerlem Mere, with steam cylinders of twelve feet diameter and fifteen feet stroke, driving eight pumps of sixty-three and seventy-three inches diameter, and ten feet stroke. These three engines were I capable of delivering a volume of water six times as great as that of the Croton. The next largest pumps are those of the Graving Dock at Brooklyn, of one-third of the capacity,of those at Haerlem Mere. The steam engines next in size are those of the Bristol and Providence steamers, with cylinders of nine feet two inches diameter and twelve feet stroke. The speaker then described the Bessemer steel process, and spoke of the changes which it is destined to produce in engineering structures Seven of the most noted modern engineering works, to : contrast with the seven wonders of the ancient world, are the Thames Tunnel, the Great Eastern steamship, the Atlantic Cable, the Britannia and Niagara Bridges, the Erie Canal, modern ordnance, and the Pacific Railway. Among the great projects of the age are those for building canals, railways, tunnels, bridges, and steamers. In canals, we have the project i of one around the Falls of Niagara; a re-enlargement of the Erie for vessels of 1,000 tuns; the Suez, nearly completed; one cross the Alleg hanies in Virginia; one through the Nicaragua i Lake or Panama, and one from Huron to Ontario. In railways, we have the Pacific on the eve of completion; the Mont Cenis in rapid progress; one across the continent from Rio Janeiro begun, and many others of magnitude. Of bridges, we have those in progress across our great Western rivers; one proposed across the East River at New York of 1,600 feet clear span ; two over the Hudson, above and below West Point; i another across the Straits of Messina, covering the " Seilla and Charybdis with clear spans of 1,000 meters (two-thirds of a j mile) each," and with piers of 700 feet high, half in and half out of the sea, and finally the modern " Pons Asinorum," a bridge project across the Straits of Dover, sixteen miles long, in clear spans of two miles each, with piers of 1,000 feet depth in the water. This project is said to be favored by Napoleon. In tunnels we have that of Mont Cenis, eight miles, and of the Hoosic, five miles in length, both in rapid progress ; one of wrought iron tubes at London, and another at Chicago, almost completed; tunnels proposed under the East and North Rivers atNew York, under the Ganges at Calcutta, and under the Straits of Dover.