Feb. 28, 1878] 



NATURE 



347 



city — say Glasgow — the head police and fire station in 

 the central district will be in direct communication with 

 the sub- stations in the northern, western, southern, eastern, 

 and St. Rollox districts, and each of these again will be 

 local centres, and command a host of street, fire, and 

 police " call " stations placed at convenient distances 

 along the thoroughfares in their respective districts. 



Another distinctive principle of the auto-kinetic system 

 is that which has already been noticed, namely, the 

 "starting" and "transmitting" wire traversing the streets 

 together. If we suppose a number of speaking stations to 

 be required along the route — say 300 — it is evident that 

 at each point where an instrument is placed the two wires 

 will require to be brought into the instrument — the one 

 to start the instrument when a communication is to be 

 sent, and the other to pick up and automatically transmit 

 that message to the district centre. We have before stated 

 that no instrument is " in circuit " except when speaking, 

 and then only during the time occupied in the transmis- 

 sion of the message. It therefore follows that at each 

 station along the line, while in a state of rest, the electri- 

 cal continuity of both the " starting " and " transmitting " 

 wire must be maintained independent of the apparatus. 



A general outline of the manner of employing these 

 two wires will explain the system. 



We will commence first with the modus operandi of the 

 *' starting " wire, then with that of the " transmitting " 



wire, and finally describe the nature of the automatic 

 apparatus by which the novel and important features of 

 the auto-kinetic system are obtained. 



Assume for a moment that the apparatus is inclosed in 

 an iron erection somewhat similar to that of a street 

 pillar letter-box, and that in the inside of this box one 

 portion of the instrument consists of an ordinary electro- 

 magnetic coil C, an armature A, and detent E working on 

 a centre e locking into a small arrangement of wheel- work 

 and barrel D, without any maintaining power ; and that 

 one end of the wire of this electro-magnetic coil is con- 

 nected permanently with the earth, the other end being 

 attached to a metallic spring s placed in position to form 

 a contact, under certain conditions, with a second spring 

 s' in connection with the " lead in " from the starting wire 

 nearest to the district sub-station. In this position as 

 regards the instrument it is a broken circuit, and of course, 

 therefore, the instrument is out of connection. If now 

 we trace the other "lead in" from the "starting" wire 

 and conceive it to be brought into the pillar-post and 

 carried up to the second spring s', and as from this spring 

 a connection exists with the " starting " wire, a continuous 

 metallic circuit is established through the pillar-box, indi- 

 cated in the illustration by the W — >■ as far as the passing of 

 " starting " electric currents is concerned from any other 

 instrument along the circuit which may have to travel the 

 wire without affecting the instrument under notice, which 



Arrangement of Circuits—" Call Station " Instrument. 



remains electrically out of circuit by reason of the break 

 in continuity at the spring S attached to the coil wire. We 

 will now advance a step further, and assume that the 

 continuity of the " lead in " of the "starting " wire furthest 

 from the district station is only maintained so long as a 

 weight v/ rests upon the two ends a and b. It will there- 

 fore be evident that were the weight w raised, the through 

 continuity zX a b maintained by the weight would be 

 destroyed, and until so far raised as to mechanically press 

 the springs s and s' together — the coil wire spring and 

 the lead in " starting " wire spring — the through circuit 

 on the starting wire is broken. Now the weight w being 

 raised what follows ? The moment that the springs s 

 and s' are brought into contact electrical continuity is 

 established between the district station and this instru- 

 ment, and the battery current flows from that station 

 along the starting wire, passing all intermediate instru- 

 ments which are necessarily out of circuit, enters the 

 electro-magnetic coil c, and throws the instrument to 

 earth as a terminal with the district centre, at once cutting 

 off all interference that might arise from other instruments 

 along the line speaking at the same time. 



Thus, for the moment that the two springs s and s' are 

 in contact, the current has entered the coil c, the arma- 

 ture A has been attracted, and the detent E being with- 

 drawn has liberated the drum D which commences to 

 revolve, having been wound up by the elevation of the 

 weight w. 



The liberation of the detent, therefore, instaatly causes 

 the weight w to descend, and the act of falling separates 

 the two springs s and s', the starting wire, as far as this 

 particular instrument is concerned, being thrown off, 

 and the through circuit also remaining broken until the 

 weight has descended and closed the contact by pressure 

 at ab. 



Before we proceed, let us suppose that during this 

 interval of time between the raising of the weight and 

 its falling, some other instrument or instruments along 

 the line had been called into requisition, what would 

 happen .? The weight w at each instrument would have 

 been raised, placing the springs S and S' in metallic 

 contact, and the instrument thrown into position ready 

 for speaking ; but as no current could pass along the 

 starting wire until continuity had been restored at the ab 

 of the first speaking instrument, which for the moment 

 had become a terminal instrument, no current could 

 enter the coil C of the second instrument ; and as 

 the detent E could not be released, the weight would 

 remain suspended, until the arrival of the currenc 

 along the starting wire attracted the armature and 

 released the drum ; in due course the second instru- 

 ment is immediately thrown off the circuit, and succeeded 

 automatically by a third, fourth, or any number along the 

 line in succession, according to their distance from the 

 district centre or battery station. It will therefore be 

 seen that as the battery current always is in readiness to 



