40 IOWA ACADEMY OF SCIENCES. 



To make the plug, take a brass rod about 3.5 inches 

 long and, say, f inch in diameter. Turn one-half of it 

 down to the size of the drill used in boring out the chan- 

 nels in the jack; point the end neatly. See Fig. 4, 0. 

 Thread the otlier half with a rather coarse screw thread. 

 Also with a drill about one-eighth inch thick bore a hole 

 a half or three-quarters of an inch deep in this end; P, 

 Fig. 4. The end of the cable R is stripped and soldered 

 into the hole P. To make the handle for the cable take a 

 piece of thick walled, hard rubber tubing about two inches 

 long, tap it out to fit the thread upon the plug, finish it 

 neatly, and screw it on the plug into the position Q, Q. 

 The other end of the cable is finished in the same way. 

 It is advantageous to slip the handle Q on the cable before 

 the latter is soldered in to the plug. The cables must, of 

 course, be long enough to reach between the jacks farthest 

 apart in the board. In the board constructed, 100 jacks 

 are arranged in ten rows, and occupy a space about 30 by 

 40 inches. 



The front of the board is protected by thin panels, with 

 holes corresponding to the channels in the jacks, and 

 admitting the plugs. 



When this style of jack is to be used in a fire-proof 

 switch board, the back of the board may be a slate slab to 

 which may be bolted small brackets or right angle pieces 

 of brass, upon which the jacks may be fastened in almost 

 identically the same manner as when wood is used. The 

 bolt, or bolts, by which the brackets are fastened to the 

 slate may serve also to connect the terminals of the cir- 

 cuits to the jacks. The front of such a board may be pro- 

 tected by panels of marble or slate, with holes properly 

 located for the admission of tlie plugs to the jacks. 



A CAMERA TABLE. 



By a camera table is here meant a device by which an 

 ordinary camera is conveniently mounted for photography 

 for scientific purposes, such as enlarging or reducing cuts, 

 charts, etc., for lantern slides or for illustrations to be used 

 in the class room, in note books, and the like; or for 



