Figure 228 shows how to connect a helix and a condenser to a coil and a spark-gap. The two clips are made by bending a strip of sheet brass and connecting a piece of flexible wire to one end. [Illustration: Fig. 224.—A Test-Tube Leyden Jar.] In large stations, the best position for the clips is found by placing a "hot-wire ammeter" in the aerial circuit and then moving the clips until the meter shows the highest reading. The young experimenter will have to tune his set by moving the helix clips about until the best results are obtained in sending. [Illustration: Fig. 225.—Eight Test-Tube Leyden Jars mounted in a Wooden Rack.] If the spark coil is a good one and capable of giving a good hot spark, it may be possible to tell when the set is in proper tune by placing a small miniature tungsten lamp in series with the aerial and changing the clips, the condenser, and the length of the spark-gap until the lamp lights the brightest. An _oscillation transformer_ is sometimes used to replace an ordinary helix when it is desirable to tune a station very closely so that its messages shall not be liable to be confused with those of another station when both are working at the same time. [Illustration: Fig. 226.—A Helix and Clip.] An oscillation transformer consists of two helixes arranged so that one acts as a primary and the other as a secondary. An oscillation helix may be made by making two sets of helix frames similar to that in Secondary Figure 226. [Illustration: Fig. 227.—An Oscillation Transformer.] The primary should be provided with eight turns of brass ribbon and the secondary with twelve. The primary supports a stiff brass rod upon which the secondary is mounted. The secondary should slide up and down on the rod but move very stiffly so that it will stay where it is put. [Illustration: AN OSCILLATION HELIX.] [Illustration: AN OSCILLATION CONDENSER.] An ordinary double-throw, double-pole knife switch having a porcelain base will make a very good aerial switch in a small station. It is used to connect the aerial and ground to either the transmitting or receiving apparatus at will. Such a switch is shown in Figure 230. [Illustration: Fig 228.—Circuit showing how to connect a Helix and a Condenser.] The aerial should be connected to the post _A_ and the ground to _B_. The posts _E_ and _F_ lead to the transmitter, and _C_ and _D_ to the receptor, or vice-versa according to which is the more convenient from the location of the apparatus on the table or operating bench. A suitable table should be arranged to place the wireless instruments upon so that they may be permanently connected together. [Illustration: Fig 229.—Circuit showing how to connect an Oscillation Transformer and a Condenser.] The Continental Code is the one usually employed in wireless telegraphy. It differs slightly from Morse as it contains no space letters. It will be found easy to learn and somewhat easier to handle than Morse.