steering cylinder and almost immediately rectifies the error of direction. As a matter of fact, the course of a torpedo controlled by a gyroscope is not a straight line, but rather a just perceptible zig-zag whose mean direction is the course set by the gyroscope.
Referring to Fig. 207, in which the more essential parts are shown dissected from their surroundings, and to the photograph. Fig. 208, the gyroscope wheel A is mounted on ball-bearings in the ring B, which is pivoted in the outer ring C, which in turn is mounted on fixed centres in the usual manner. The rotary valve is not actually mounted on the outer ring trunnion as described, but is operated by a pin P projecting upward from the outer ring arranged to engage in a slot in the lever L fixed to the valve V, the end of this lever being so formed that the valve is capable of being moved through a certain definite range and no more, any further motion of the torpedo away from its prescribed course being without effect. The air is controlled to and from the steering piston, contained in the cylinder S, by passages in the cylindrical valve V; this valve is of small size, and but little force is required to move it one way or the other.
The effect of the little resistance that the valve offers is to cause a precession of the gyroscope about the trunnion axis of the inner ring B, without any appreciable yielding of the outer ring C; consequently the course is not in the least affected by valve-friction. The course could only become involved if the precession were to continue until it could go no further, as when the ring B reaches the limit of its motion, or, if no stops exist, until the axis of spin becomes coincident with the mounting of the ring C. Under the conditions of service such a contingency never arises, the total "flight" of a torpedo occupies but a few minutes, and as it has at the worst but little "bias" one way or the other, the reactions the gyroscope experiences are sometimes in one direction and sometimes in the other; consequently the precessional movements in great part correct each other, and
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