Page images

of every scientific academy of Europe. The degree of Doctor of Laws was conferred upon him by the Universities of Edinburgh and Dublin, and he was also admitted to the freedom of those cities. The Order of Knight of the Red Eagle of Prussia was conferred upon him by the king of Prussia.

Since 1833 his publications have been very numerous. Among them are works on the Echinoderms and on the Fossil Mollusks of the Jura, a German translation of Buckland's Geology, with copious notes, and his Fresh-water Fishes of Europe. The Nomenclator Zoologicus, published some years since, and the Bibliographie Générale d'Histoire Naturelle, lately published by the Royal Society, are the product of several years' observation.

In 1837 Agassiz first promulgated his "Glacial Theory," which has ever since attracted much attention. It having been asserted that it was inconsistent with known facts, Agassiz for eight years spent his summer vacations in making observations at the Glacier of the Aar, eight thousand feet above the sea, and twelve miles from any other habitation than his own hut. The result of these examinations are contained in two works, Etudes sur les Glaciers, and Système Glacière.

In 1846 Agassiz came to America, and on the establishment of the Lawrence Scientific School he accepted the appointment of Professor of Zoology and Geology, which he still holds. Since his arrival in this country, Professor Agassiz has presented a large number of communications to the American Academy and other scientific bodies, and has published, in connection with Dr. Gould, of Boston, a Zoology for students. His elaborate work on Lake Superior has just appeared.

[merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small]





FROM the report of the engineer who has charge of the Wheeling Suspension Bridge, we derive the following facts. The span of the bridge from centre to centre of the supporting towers is 1,010 feet, which is 152 feet longer than the bridge at Friburg in Switzerland, the longest span hitherto constructed. The height of the flooring is 97 feet above the low-water level of the river, and 58 feet above the highest flood ever known, except the celebrated one of 1832. The towers over which the suspension chains pass are built upon the abutments, and that at the eastern side rises 153 feet above low-water, and 60 above the abutments; the other tower varies slightly from this measurement. The wire cables which support the flooring are 12 in number, 1,380 feet long, and 4 inches in diameter. These cables rest on iron rollers, placed on the summits of the towers, the movements of which will relieve the towers of the strain consequent upon the contraction and elongation of the wires, occasioned by the changes of temperature. The flooring is 24 feet wide, divided between a carriageway of 17 feet, and two footpaths of 3 feet each. The length of the wood-work resting on the cables is 960 feet, and its weight is 546 pounds per lineal foot, making a total of 524,160 pounds, or 262 tons. În each cable there are 550 strands of No. 10 wire. The weight of each lineal foot of the 12 cables, which are composed of 6,600 strands, is 330 pounds, making, with the weight of the timbers, bolts, &c., a total of 920 pounds per lineal foot, or 634 tons as the permanent weight of the bridge. But, in addition to its own weight, it is intended to support the largest weight that can be brought upon it at one time. If filled from one end to the other with a double row of the heavy wagons used on the National Road, it is calculated that an additional weight of about 600 tons might possibly be brought upon it. But it is ascertained by a machine, that the aggregate strength of the 6,600 strands

of wire composing the 12 cables is 4,950 tons, so that they will in an ordinary state of the bridge be capable of supporting five times the strain which they are actually called upon to bear; and when the platform is filled with loaded teams they will have the power of resisting three times the strain produced by the bridge itself, and three times the additional strain produced by the teams. The anchorage of the bridge is formed on the Wheeling side by very heavy anchoring-irons, which are imbedded in the earth, and surrounded on all sides by a ponderous pile of massive masonry. On the island side, continuous links of wrought iron are imbedded in the massive wing walls, so that there need be no apprehension of a failure in this portion of the structure. This bridge was built by a joint stock company, who have a charter from the State of Virginia, and the engineer is Charles Ellet, Jr.




THE chief peculiarity of this bridge consists in its iron arch, which is extended to a very considerable span, and furnishes a highly important test of the powers of resistance, both of the material itself and of the particular form in which it is used. At the same time it is perfectly safe, for if the arch fails, the truss without is sufficient to sustain any weight that can come upon the bridge. The general arrangement of the truss is that of the well-known Howe Bridge. The arch is constructed of a centre rib of cast iron, 7 inches deep, with upper and lower horizontal flanches, 5 inches wide; two rolled iron plates are placed on the top and two on the bottom of the cast rib, breaking joint with the rib and with each other, and secured by clamps at proper intervals. Below the chords are solid cast-iron skew-backs, and castings of suitable form to connect with the skew-back and to receive the ends of the arch are placed on the top of the lower chord. As it was believed that the failure of cast-iron bridges generally results from the inequality of pressure upon the joints, they were separated to the distance of one fourth of an inch, and spelter was poured into them in a melted state. The castings were made with inch holes near the ends, through which rods were passed to assist in raising them. The most important advantage to be derived from the peculiar arrangement exhibited in this structure was the practical test of the power of resistance of a counter-braced iron arch on a large scale. The counterbraces being placed above the arch, and resting against it by adjusting or set screws, and there being at short distances vertical posts of oak, also terminating in a set screw resting on the arch, it will be readily perceived, that, by loosening the counter-brace screws, and tightening those on the posts, the bridge will be raised upon the arch, so that the latter will bear the whole weight of the truss and its load. This experiment has thus far proved entirely successful, and shows that the counter-braced arch, which is the lightest and cheapest system possible, is also perfectly reliable for spans of any magnitude. In the Franklin Institute Journal for September, from which we abridge this

« PreviousContinue »