MECHANICS AND USEFUL ARTS. 



65 



connected with the throttle valve or cocks in the feed pipe. The 

 object of this apparatus is to regulate the quantity of water to be 

 supplied to the boiler by a pump, so as to maintain the water in the 

 boiler at a proper level. As the small vessel spoken of communicates 

 with the steam chamber and the water in the boiler, it receives both 

 steam and water, the latter being always at the same level as that of 

 the boiler. It is balanced on a centre in such a manner that when 

 the water in the boiler is at the proper line, it remains poised on its 

 centre, and keeps the throttle valve in the feed pipe open to the exact 

 width that will supply the boiler with water commensurate to the 

 steam used. When the water in the boiler falls below the proper line, 

 the water in the small outside vibrating vessel diminishes, which 

 causes it to rise and open the throttle valve somewhat wider, and let- 

 ting more water to the boiler. The reverse action takes place when 

 the water in the boiler rises above the proper line. The vibrating 

 outside vessel is guided by the amount of water in the boiler to regu- 

 late the throttle valve. Scientific American. 



RAILROADS OF THE UNITED STATES, AND OTHER COUNTRIES. 



The number of miles of railway now in operation upon the surface 

 of the globe, is 29,606; of which 15,436 miles are situated in the 

 Eastern Hemisphere, and 14,170 are in the Western, and which are 

 distributed as follows : 



In the United States, 13,586 



In the British Provinces, 173 



In the Island of Cuba, 359 



In Panama, 22 



In South America, 30 



In Great Britain, 6,976 



In Germany, 5,340 



In France, 1,831 



In Belgium, 532 



InRussia. 422 



In Sweden, 75 



In Italy 170 



In Spain, 60 



In India, 30 



The longest railway in the world is the New York and Erie, which 

 is 467 miles in length. 



The total number of railways in the United States, in operation and 

 in course of construction, is 372, constructed at a cost of $400,713,907. 

 Merchants Magazine. 



RAILROAD IMPROVEMENTS. 



French's Improvement for overcoming Grades. This invention con- 

 sists of a common wooden superstructure, with a flat bar-rail : the 

 ends of the cross-timbers are cut off flush with the sleepers, and the 

 flat bar resting on the sleepers projects over on the outside of the 

 track, forming a clear continuous space on each side of the road for 

 friction rollers, or small wheels to revolve up against the projecting 

 edge of the rail. The cranks are attached to the ends of the driving- 

 axle, and between these and the driving-wheels is suspended from the 

 axle, on each side, a friction roller, or wheel, which is made to drop 

 at pleasure directly under the driving-wheels. Using the driving-axle 



