A method for operating reversing gear using steam power first introduced by James Stirling in 1874. Two cylinders, one steam and one oil and connected by a rod, were mounted outside the boiler. Often they were fitted inside the cab or housed in an extension of the driving wheel splasher but, if free standing outside the boiler, they looked similar to and could be mistaken for a Westinghouse air brake pump. The reverser is controlled by two levers in the cab. To move the reverser, steam is admitted to one side or the other of a piston in the steam cylinder. The piston moves the rod and thus varies the reverser rod position. A separate valve controls the flow of oil in the second cylinder between the two sides of the piston. When the position of the reverser is set by the steam cylinder, it is locked by the oil cylinder. A pointer in the cab provides an indication of the position of the reverser. Single lever controls were later provided for some versions of this and other types of power reverser. Steam reversers were generally difficult to maintain and were prone to "wandering" off position due to the escape of steam or the leakage of air into the oil cylinder. They often required a degree of "persuasion" or repeated operation to get the reverser set in the correct position.