Part 8 (1/2)

It is on this principle that impulses are sent for thousands of miles, and no doubt they extend even farther, if the proper mechanisated

THE COHERER--The instru these ienerally called a _coherer_, although detector is the term which is most satisfactory The name coherer comes from the first practical instru 75_ WIRELESS TELEGRAPHY COHERER]

HOW MADE--The coherer is silass, within which is placed iron filings When the oscillations surge through the secondary coil the pressure or potentiality of the current finally causes it to leap across the ss and, as it were, it welds together their edges so that a current freely passes The bringing together of the particles, under these conditions, is called cohering

Fig 75 shows the simplest form of coherer The posts (A) are fir screw (C) in its upper end, and these screardly against and serve to bind a pair of horizontal rods (D), the inner ends of which closely approach each other These ether or as far apart as desired E is a glass tube in which the ends of the rods (D) rest, and between the separated ends of the rods (D) the iron filings (F) are placed

THE DECOHERERS--For the purpose of causing the s to fall apart, or decohere, the tube is tapped lightly, and this is done by a little object like the clapper of an electric bell

In practice, the coils and the parts directly connected with it are put together on one base

THE SENDING APPARATUS--Fig 76 shows a section of a coil with its connection in the sending station The spark gap rods (A) ether or farther apart, but they must not at any time contact with each other

The induction coil has one terminal of the priraph key, and the other post of the key has a wire connection (C), with one side of a storage battery The other side of the battery has a wire (D) running to the other ter 76_ WIRELESS SENDING APPARATUS]

The secondary coil has one of its ter post has an adjustable rod with a knob (F) on its end, and the other binding post (G), which is connected up with the other ter rod with a knob (H)

From the post (E) is a wire (I), which extends upwardly, and is called the aerial wire, or wire for the antennae, and this wire also connects with one side of the condenser by a conductor (J) The ground wire (K) connects with the other binding post (G), and a branch wire (L) also connects the ground wire (K) with one end of the condenser

[Illustration: _Fig 77_ WIRELESS RECEIVING APPARATUS]

THE RECEIVING APPARATUS--The receiving station, on the other hand, has neither condenser, induction coil, nor key When the apparatus is in operation, the coherer switch is closed, and the instant a current passes through the coherer and operates the telegraph sounder, the galvanometer indicates the current

Of course, when the coherer switch is closed, the battery operates the decoherer

HOW THE CIRCUITS ARE FORMED--By referring again to Fig 76, it will be seen that when the key is depressed, a circuit is forh wire B to the prih wire D The secondary coil is thereby energized, and, when the full potential is reached, the current leaps across the gap for up a disturbance in the ether which is transh space in all directions

It is this impulse, or disturbance, which is received by the coherer at the receiving station, and which is indicated by the telegraph sounder

CHAPTER XII

THE TELEPHONE

VIBRATIONS--Everyof the heart, the action of the legs in walking, the winking of the eyelid; the iht; sound, taste and color appeal to our senses by vibratory means, and, as we have hereinbefore stated, the netisths

THE ACOUSTIC TELEPHONE--That sound is merely a product of vibrations may be proven in many ways One of the earliest forms of telephones was simply a ”sound” telephone, called the _Acoustic Telephone_ The principle of this may be illustrated as follows:

Take two cups (A, B), as in Fig 78, punch a s or wire (C) from the hole of one cup to that of the other, and secure it at both ends so itinto the cup (A) the bottom of it will vibrate to and fro, as shown by the dotted lines and thereby cause the bottom of the other cup (B) to vibrate in likeit will receive not only the same amplitude, but also the saave forth

[Illustration: _Fig 78_ ACOUSTIC TELEPHONE]