MECHANICS AND USEFUL ARTS. 3 



three o'clock A. M. and P. M. These and other interesting results, as 

 indicating the safe working of the great machine, are read by means 

 of self-registering thermometers that record the constant temperature, 

 placed in mahogany cases, protected by plate glass, and under lock 

 and key. There is also a self-acting clock-work apparatus that ele- 

 vates a shaft on a vertical plane, all the minutest motions of the tubes 

 being delineated by an arm carrying a pencil, which is fixed to the 

 tube. If a compass be held over any part of the bottom of the cells, 

 the south pole is affected, and if held over the top of the cells, the 

 north pole is affected, and this effect is observable in all parts of the 

 tube, whether at the centre or end, although their position is only 

 about 10 W. of the magnetic meridian." 



Some of the acoustics effects produced by the bridge are curious. 

 The report of a pistol fired beneath it is repeated three or four times 

 The cells of the top and bottom form excellent speaking tubes, and, 

 by elevating the voice, persons may converse through the entire length 

 of the bridge, more than 500 yards. If one end of the cells be closed 

 they return a powerful echo ; but, although a whisper is thus dis- 

 tinctly repeated, the loudest whistle does not appear capable of return- 

 ing any echo. 



REMINGTON'S BRIDGE. 



A YEAR or two since considerable interest was excited by the pub- 

 lication of a letter detailing the struggles and trials of a young Ameri- 

 can in London, named Remington, who was striving to introduce a 

 new bridge of his invention, for which extraordinary merit was 

 claimed. Some doubt was afterwards thrown upon the whole story, 

 but Mr. Remington has since returned to this country, and erected a 

 bridge on his plan at Montgomery, Ala., which is thus spoken of: 

 " This beautiful structure, apparently too fragile to sustain its own 

 weight, proves to be all that has been claimed. It was, immediately 

 after the scaffolding was removed, put to the severest test. Hundreds 

 of people passed over it, and it was conceded by the most skeptical 

 that it would stand and answer for all practical purposes. The bridge, 

 which at a little distance resembles a slight ribbon or shaving of wood, 

 extended over a ravine beneath, four or five hundred feet in length, 

 though looking as if it could not bear the pressure of a bird, is found to 

 endure immense weight ; in fact, it appears, all that can conveniently 

 be placed upon it. The planks, which are at the abutment about six 

 inches thick, fine away towards the centre to about one inch, or an 

 inch and a half, and are finally joined by an impervious cement, the 

 invention of Mr. Remington. The deflection in the centre is about 

 ten feet." 



The Scientific American, for July 20, notices a model of Remington's 

 plan. It is 160 feet long, composed of four stringers, of a little over 

 two inches square at the abutments, and tapering to about an inch 

 square at the centre. It is of the form of an inverted arch. The 

 stringers are made of several pieces of white pine, joined together by 

 a scarf-joint, their ends, when they are joined,, being bevelled at a 



