The circuit-closer consists of a cylindrical brass casting, having one end closed, and on this end are four feet by which it is secured to the lower head of the service torpedo by screws. The cylinder, 4¾ inches long and 5 inches in diameter, is closed at the open end by a screw-cover, having four lugs that serve as bearings for the contact-arms; these arms, four in number, work in slots cut in a plunger that passes through the center of the cap, and they are held in place by screws through the ends of two arms and their lugs. Inside the cylinder are two insulated contact-springs secured to binding-posts in an ebonite collar. This collar screws on the end of a short brass tube that carries a plunger tipped on the inner end with ebonite. A stout spiral spring in the tube through which passes this plunger, maintains, normally, the end of the plunger clear of the contact-springs. A rubber diaphragm separates the plunger in the cover from the plunger in the tube, and also acts as a washer to the cover, making the cylinder water-tight; a brass washer, laid on this diaphragm, acts as a friction-plate for the cover to turn on when screwed up. A safety-pin through the outer plunger prevents its being forced in accidentally. When this pin is withdrawn, any pressure on the contact-arms tends to force the inner plunger in against the action of the spiral spring and to close the break between the contact-springs. The break is ³/₁₆ inch and the tension of the spiral spring is 75 lbs. On the side of the cylinder is fitted a stuffing-box furnishing a water-tight entrance for the leading-wires to the binding-posts of the contact-springs. The circuit-closer, complete, weighs 7 lbs. SECONDARY SPARS. =Pattern A.—Plate IV.= (One is furnished for each Service Torpedo.) These are iron pipes, 8 feet long. Those for ships‘ use have a slot cut in one end, for a key. Those for use in boats are fitted at one end with an iron disc, called a butt, and at 2 feet 2 inches from the butt an iron cap is riveted to the spar. All secondary spars have, at 5 inches from the outer end, a hole for the torpedo-pin. Secondary spars are packed six in a box; those for ships having a key stopped to each to be used in securing the secondary spar to the inner spar-band; those for boats having a toggle stopped to each to be used in securing the secondary spar to the boat spar. TORPEDO PINS. =Plate IV.= Torpedo pins are short iron pins with an eye in one end, to which a spun-yarn tail is spliced, designed to secure torpedoes to secondary spars. One is provided for each service and exercise torpedo. They are packed, with the spindles, in Box 53. REEL BOX.