Within a radius of IO to 20 miles or more, it is not a matter of theoretical speculation, but a result of actual facts, extend ing over a period of many years' experience, that compressed air can be economically produced, conveyed, and utilized as a motive power; and if this power is to be distributed through out a number of buildings or factories, or in the interior of a mine, the absolute safety consistent with the use of compressed air is an element of superiority to which the electrical trans mission has no possible claim. However well insulated the conductors may be, the vicinity of a dynamo is always dangerous, either on the ground of fire or of bodily injury. In a large power station, manned by a picked staff of attend ants, this danger is small indeed; but the conditions are alto gether different if the motor is under the care of a miner or of an ordinary workman.