also customary in calculating the heating surface Hedgehog Transformer

—A form of of tke shell, to consider that two-thirds of it is exposed to the action of heat. For internal fire transformer devised for reducing the iron box boilers twelve square feet heating surface is lo , having its coils wound upon a core usually allowed per horse power consisting of a bundle of iron wires with their ends spread out like the spines of a feat Insulator.—Any substance which hedgehog, so that the lines of force pa acts as a non-conductor of heat. partly through the iron and partly through the air. feat Lightning.—Lightning visible in broad flashes near the horizon and unac- | Heeling Error of Compa Needle.— companied by thunder, observed when a A further deviation, due to the magnetism storm is at a great distance. of the ve el, to which a ship’s compa is liable when the ship is rolling.