Our next addition was a telegraph sounder as shown in Fig. 195. _B^{1}_ is a single dry cell, _C_ is the coherer, _R_ is the relay, _B^{2}_ is now a battery of three cells. Part of its current goes to _B^{3}_, the tapper for the coherer, and part of its current goes to the electro-magnet of the telegraph sounder _S_. Ordinarily a spring holds the iron strip _d_ up against the metal stop _a_, but when the current passes through the electro-magnet it pulls down this iron strip with a click against the metal stop _e_. But while this is happening _C_ is being tapped by _B_, and is ready to respond to each wave. It was only necessary now to have some code of signals in order to communicate by telegrams. We learned the system of dots and dashes, or short and long periods marked off by the sounder, which all telegraphers use and which is known as the Morse alphabet, and very soon Harold and I were telegraphing from one room to another messages of several sentences at a time, the Morse alphabet being told off on the spark coil and being received through the coherer and telegraph sounder. It was not long before Harold and one of the neighbours' boys were exchanging messages between their homes, each having a spark coil and the necessary receiving apparatus, and having extended their antennæ to the top of the buildings into what are called in the wireless language _aerials_. [Illustration: Photograph by Helen W. Cooke. Induction Coil of a Wireless] The fever for wireless telegraphy spread like wild-fire among the boys. In a few months they had formed a "wireless club." They had each read anywhere from ten to thirty books and articles upon the subject, and had secured the latest improved apparatus. They made it a practice to spend hours daily at their instruments picking up and keeping on file messages which were sent to and from steamers leaving the harbour for European ports. On one occasion they showed me from these files scores of messages--fond, personal, and supposedly private farewells to friends and communications between business partners which they would never have made on land without first closing the office door. The boys had acquired a mass of technical knowledge upon the subject which far exceeded my comprehension. But their teachers in school complained that they would learn nothing else, and some of the boys had already received warning that they might fail of promotion.