When wireless signals pass through the relay they will cause the resistance to drop and allow sufficient current from the dry cell to pass through the coherer to energize the magnets of the relay and draw the armature in, thus closing the decoherer circuit. When the armature of the relay is drawn in towards the magnets the relay contacts are brought together. This closes the decoherer circuit and starts the hammer to tapping the coherer, thus restoring the filings to their former loose state. The decoherer will tap the coherer as long as the incoming signals continue. By breaking the signals up into dots and dashes of the telegraph code a message may be easily transmitted and read from the tapping of the decoherer. [Illustration: FIG. 166.—Coherer, Decoherer and Relay Connections.] 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. [Illustration: FIG. 169.—Details of Spark Gap.] The coherer will be found to be the most sensitive when only a very few filings are used. The adjustment desired in the relay is the one in which the armature is given the smallest possible amount of motion and the spring which pulls the armature away from the magnets, the least tension.