MECHANICS AND USEFUL ARTS. 39 



The weight of the structure decreases in a geometrical ratio as the 

 distance from the towers increases, so that at the centre, though the 

 full strength of the stringers and the direct arch below them is retained, 

 the weight of the structure is diminished to an exceedingly low point. 

 As to economy of construction this bridge can be surpassed by none, 

 especially where a great span is required. There is no heavy timber, 

 the entire structure being built of plank and boards. No piers are 

 necessary, the only stone work being the laying the abutments, etc. 



The. manner of constructing the stringers speaks well also for their 

 durability, being put together with oil cement between each board 

 which will render decay next to impossible ; it is very well known 

 that wood prepared in this way has been excavated from the ruins of 

 old cities, after being buried more than three thousand years, in a state 

 of perfect preservation. Railroad Journal. 



FLYING RAILROAD BRIDGE. 



THE Scientific American states that C. B. HUTCHEXSOX, of Water- 

 loo. X. Y., has invented and taken measures to secure a patent for a 

 valuable improvement on Railroad Bridges for navigable waters. 

 The object of the invention is to have a bridge perfectly open and 

 free at all times for vessels to pass, except the few minutes required 

 for a train to pass over, and to carry over trains expeditiously and 

 safely. A certain number of piers or abutments are built in the river, 

 with space between them for the passage of vessels. Instead of having 

 a stationary platform to the roadway extending across on the piers, 

 he employs a flying or running platform, which carries the train 

 spanning and springing over the successive spaces between the piers 

 from the one side to the other. There are tracks or rails on all the 

 piers, and on the flying platform there are wheels that run on the 

 tracks, like a long railroad car. The length of the flying platform is 

 in proportion to the width of space between the abutments, so that it 

 will be impossible to overbalance it while springing from one pier to 

 the other like a sliding drawer. The flying train is stationary at one 

 side or the other, when the train is not passing. It is to be propelled 

 across by having stationary power on itself, or to have it so constructed 

 that the locomotive of a train may propel it across. It may be called 

 " a flying railroad bridge." 



THE GENESEE HIGH BRIDGE. 



THE bridge by which the Buifalo and ]^ew York Railroad crosses 

 the Genesee river, near Portageville, is one of the most gigantic 

 structures in this country, being eight hundred feet in length, and 

 two hundred and thirty-four feet above the stream. About one hun- 

 dred feet below the bridge is a perpendicular fall in the river of 

 sixty-six feet; hence, from the top of the bridge to the bed of the 

 river below the fall, it is three hundred feet. The Genesee High 

 Bridge towers above all similar structures in America ; even the sus- 



