Wireless Telegraphy and Telephony

64 WIRELESS TELEGRAPHY to be moisture proof. Bare wire is preferable to all forms of insulated wire. The coil is usually three to four inches in diameter and eight to twelve inches long. Tuning coils are known as “single slide,” “double slide” and “three slide” according to the number of contacts they are fitted with. The loading coil is a supplementary tuning coil used to furnish extra inductance in case it is desirable to obtain a greater range of resonance or tuning. Fig. 8o.—Fixed condenser. It is merely a single slide tuning coil connected in series with the regular tuning device. It is not always a neces- sity but is often part of the equipment when it may be necessary to adjust the apparatus to receive long wave lengths. Condensers are devices for collecting and storing elec- tricity. They play a very important part in both the trans- mitting and receiving operations. Condensers and Leyden jars have already been described in connection with the transmitting apparatus. The condensers used in receiving are very much smaller in size and capacity but are the same in principle. There are two general types of receiving condensers called “fixed” and “variable” accordingly as the capacity is alterable or not.