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Page:Popular Science Monthly Volume 90.djvu/487

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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.

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