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STRENGTH OF RAILS.

to break, when subjected to sudden blows, andits strength is considerably affected by theunavoidable occurrence of air-bubbles, andother imperfections in its organization; yetstill we are enabled to form a Rail-road withit, on which weights of considerable magni-tude can be conveyed, without much risk ofbreakage.

It is a consideration of paramount import-ance, in the construction of a Rail-road, toform it of such materials as combine strengthand durability with economy. Cast-iron, whileits hardness presents a surface that opposeslittle obstruction to the wheels of the car-riages, forms a substance which is also verydurable, and resists the action of the wheelswith oreat effect. Its brittleness forms the

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only source of reasonable objection ; and, asthat cannot be obviated without increasing thesection of the rail, and adding to the weight,and consequently to the cost, has lately pro-duced an innovation in the material, in thesubstitution of a particular form of malleableiron-rails, the tenacity of which resisting sud-den fracture, therefore obviates the danger,inconvenience, and cost of the breakage ofcast-iron.

In describing the different kind of rails,used in the construction of Rail-roads, I have