IOWA ACADEMY OF SCIENCES. 39 



motions differing in frequency by an octave. One variety 

 of this curve is shown in Fig. G. 



A SIMPLE AND EFFICIENT CABLE SWITCH BOARD. 



A serviceable, cheap, and easily constructed switch 

 board, which has been in use for several years, has a jack 

 of novel design. These jacks are, in the switch board in 

 question, mounted on a wooden frame. This is proper 

 enough where the circuits terminating in the board are 

 subjected to pressures of only a few volts, as in connecting 

 batteries and apparatus for the ordinary purposes of a 

 physical laboratory. Bat where an indestructible board 

 is required, the jacks in question can readily be mounted 

 on slate or marble. 



To make the jack, take a common heavy brass hinge 

 three inches wide, and cut it in two like halves along the 

 line AKLB, Fig. 1. Now fold the leaves of one-half 

 together until they are parallel, clamp it in a hand-vise, 

 with a plate of proper'thickness between the edges of the 

 leaves. With a drill three-sixteenths inch in diameter bore 

 the hinge out near the joint, so as to make the channels 

 HK and IL, to receive the round plug of the cable, which is 

 to be used in connecting different jacks in the switch board. 

 Bore the extra hole Gr. The jacks may be mounted upon 

 horizontal bars forming the frame-work of the board. A 

 scre.w is driven through the hole A so as to fasten the jack 

 down to the bar, with the end I nearly flush with its front 

 edge. A round headed screw in G will serve to keep the 

 leaf AH from closing down too closely upon BI, but 

 leave room for the easy insertion of the plug. 



Another screw through E will also serve to fasten the 

 jack to the bar. The terminal of the circuit coming to 

 this jack may be clamped to the hinge by the same screw. 

 The hinge is now closed by folding the opposite leaf over. 

 A spiral spring of a few turns of spring brass wire is 

 slipped on a rather long screw, which is then driven 

 through the holes F and D, into the wood, until the spiral 

 spring presses the upper leaf of the hinge down firmly. 

 See Fig. 8. The jack is now complete. 



