Popular Science Monthly 



471 



wire of the lo-in. cylinder is connected to 

 •one of the terminals. The top end of 

 wire of the lo-in. cylinder 

 is connected to the lower 

 end of wire on the 8-in. 

 cylinder, the connection 

 being made at the bottom. 

 Enough wire has to be left 

 at the top of all cylinders 

 so that this connection can 

 be made. Care must be 

 taken that the wire does 

 not come in contact with 

 any metal at any point. In 

 the same way connect the 

 windings of the 8-in. and 

 6-in. and of the 6-in. and 

 4-in. cylinders. The top 

 end of the wire on the 

 4-in. cylinder is brought 

 out to the other terminal. 

 The two terminals may be 

 placed near the bottom of 

 the i2-in. cylinder. Drill 

 through two 34-in- holes 

 and insulate two terminal 

 posts in these holes and tighten them. 

 The wires from the heater leading to the 

 terminals can be connected on the inside 

 and from the outside the socket connec- 

 tions can be made. The terminals from 

 the positive pole of ordinar>' dry bat- 



A loop is made for starting 

 wire and coil on cylinder 



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Pattern for cutting and drilling the legs 

 or stand pieces that hold the cylinders 



teries can be used. Drill the two J^-in. 

 holes about 2 in. apart at any convenient 

 place near the bottom. Insulate the 

 terminals with hard rubber or fiber. 

 After this is done place on the cover plate 

 and the heater is readv for use. 



ionized gas collects between the sparking 

 points, the breakdown voltage of the 

 gap will be reduced and 

 sparks will pass premature- 

 ly. The same unfortunate 

 result occurs when the 

 electrodes become over- 

 heated and tend to produce 

 arcs. The effect of such 

 irregular sparking is to re- 

 duce efficiency and to make 

 production of a clear signal- 

 tone impossible. 



The drawing shows a 

 form of spark-gap devised 

 by H. Shoemaker and dis- 

 closed in U. S. Patent 

 1,170,853 for 1916. The 

 usual alternating-current 

 transmitting circuits are 

 used, in which power from 

 the generator 20 is led 

 through key 21 to step-up 

 transformer 22-23. The 

 secondary charges condens- 

 er 13, which oscillates 

 through primary 12 with variable top 

 15 and spark-gap 9, 10. 



The antenna 16 and ground 19 are 

 coupled through secondary 17. 



The novel feature of this transmitter 

 is that between the stationary gap 

 electrodes 9, 10 is inserted a rotary 

 disk of mica, glass, porcelain or some 

 other such insulator, pivoted on shaft 3 

 and supported in bearings i, 2 as shown. 

 At equal distances around the disk, and 

 a few inches from the outer edge, are 

 drilled a series of holes such as indicated 

 at part 7. These holes pass in front of 

 the spark-gap electrodes, and sparks can 

 pass only when a hole is directly between 

 9, 10. Thus, by rotating the drilled 

 insulating disk the effect of a rotary 



New Patent on Interrupter 

 Spark-Gap 



A ROTARY spark-gap, or one upon 

 which a cooling air-blast is blown, 

 is generally more regular in operation 

 than a simple open stationary-electrode 

 device. To secure uniform sparking, the 

 condition of the gap and the electrodes 

 must remain constantly the same. If 



A mica disk with holes is rotated between 

 the gap electrodes, assuring an even spark 



spark-gap may be had without any 

 difficulties of insulating moving parts. 

 The disk may be driven by an electric 

 motor. The patent suggests making it 

 a sort of air-driven turbine. 



