Since the time of these early experiments, various other modes of detecting the existence of electric waves have been found out in addition to the spark-gap which he first employed, and the results of his observations, the earliest interest of which was simply that they afforded a confirmation of an abstruse mathematical theory, have been applied to the practical purposes of signalling over considerable distances (see Telegraphy, Wireless).
Theoretically for a given outside diameter of core the greatest speed of signalling through a cable is obtained when the diameter of the conductor is 606 (1/,/e) the diameter of the core, but this ratio makes the thickness of the guttapercha covering insufficient for mechanical strength.
In this the tongue of the relay is kept over to the spacing side by means of a current flowing in one direction, but on the depression of the signalling key the current is reversed, moving the relay tongue over to the marking side.
If the positive is called the signalling current, the line will be charged positively each time a signal is sent; but as soon as the signal is completed a negative charge is communicated FIG.
The actual speed or rate of signalling is given approximately by the formula, S = 120/ (KR), where S is the number of words per minute, R the total resistance of the conductor in ohms, and K the total capacity in farads.
The explanation of the action of the shunt is that all slowly varying currents affect the coil of the receiving instrument and its shunt in inverse proportion to their respective resistances; whereas with the comparatively rapid variations of current used in signalling the coil is forced at the beginning of each element of A v
In this manner Trowbridge showed that signalling might be carried on over considerable distances by electric conduction through the earth or water between places not metallically connected.
To stray " earth currents," and very good signalling was established between the mainland and the rock.
At each signalling station was erected an insulated metallic surface facing and near to the ordinary telegraph wires.
Lodge, Signalling through Space without Wires, 3rd ed., p. 73, 1899.
In the primary circuit of the induction coil I he placed an ordinary signalling key K, and when this was pressed for a longer or shorter time a torrent of electric sparks passed between the balls, alternately charging and discharging the elevated con-.
Lodge, Signalling across Space without Wires (3rd ed.
In the first place it increased the visibility of the signalling instrument; in the second place it brought that instrument into the position in which it could most readily catch the operator's eye; and finally it eliminated the effort involved in associating one piece of apparatus with another and in finding that other.
With the adoption of relays the signalling between the subscribers and the exchange became automatic, and, with the introduction of the principle of double and automatic supervision on the cord circuits, it became possible for the operators to tell at any instant the state of a connexion.
The large modern trunk exchanges are equipped with relays and lamps for signalling purposes.
A complete system of signalling by night and day on the Morse system is worked by the police.
The inspections made by the officers of the Board of Trade under this act are very complete: the permanent way, bridges, viaducts, tunnels and other works are carefully examined; all iron or steel girders are tested; stations, including platforms, stairways, waiting-rooms, &c., are inspected; and the signalling and " interlocking " are thoroughly overhauled.
In certain respects, on the other hand, America has gone further than the United Kingdom, especially in the matter of automatic signalling, and in the operating of points and signals by electrical power or air-pressure instead of manual labour.
Again, if the speed is low and the trains infrequent, the signalling arrangements may be of a very simple and inexpensive kind, or even dispensed with altogether.
Between 1858 and 1868 he was employed in home waters on a variety of special services, chiefly connected with gunnery, signalling and the tactical characteristics and capacities of steam warships.
Among the subjects to which he especially directed his attention were the explosive force of gunpowder, the construction of firearms, and a system of signalling at sea.
High) which contains a fine peal of bells and also serves as a signalling tower.
The Peak lies immediately to the south-west of the capital, in the extreme north-west corner of the island, and is used as a station for signalling the approach of vessels.
Services; the balloon establishment; the detention barracks; fire brigade stations; five churches; recreation grounds for officers and men; schools; and especially the military technical schools of army cooking, gymnastics, signalling, ballooning and of mounted infantry, Army Service Corps, Royal Army Medical Corps and veterinary duties.
Many novelties, too, such as the field telegraph, balloons and signalling, were employed.
SIREN, a name derived from the Greek Sirens (see below) for an acoustical signalling instrument specially used in lighthouses, &c. (see Lighthouse), and applied by analogy to certain other forms of whistle.
It possesses depots for artillery and mines, a meteorological observatory and a signalling station.
Telephones had broken down; the mist prevented signalling, and despatch riders do not seem to have been employed.