The best results are secured from a coherer outfit if it is connected to the aerial and ground by substituting it for the detector in a circuit employing a double slide tuning coil and a fixed condenser. The two wires that would ordinarily be connected to the detector terminals are simply connected to the coherer posts.
When the apparatus is to be used for demonstration or experiment and the transmitting and receiving stations are both located in the same room or house it will not be necessary to use an aerial and ground but merely to attach two copper wires about 18 or 24 inches long to the opposite sides of the coherer as shown in Figure 163.
In such a case the transmitter should be arranged as in Figure 167.
A spark gap made especially for this purpose is illustrated in Figure 168. Some of the details of the gap are shown in Figure 169.
[Illustration: FIG. 167.—How the Transmitter is Connected.]
The ball may be made in the form of a complete sphere or else consist simply of half of one as illustrated. It should have a radius of about five-eighths of an inch and arranged so that it may be mounted upon the end of a "catch-wire."
[Illustration: FIG. 168.—The Complete Spark Gap.]
The "catch-wires" are mounted in two standards similar in construction to a large binding post three and one-quarter inches high. The standards should be mounted by screwing them on top of the secondary terminals of the spark coil. The spark balls should be adjusted so that the distance between them is not over one-eighth of an inch.
The coherer apparatus will probably require to be very accurately adjusted before it will work properly.
Patience and a little experience will soon enable one to overcome the difficulties and to put the apparatus in sensitive condition without much trouble.