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LIGHTNING

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Originally appearing in Volume V16, Page 675 of the 1911 Encyclopedia Britannica.

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LIGHTNING . CONDUCTOR, or LIGHTNING See also:

ROD (See also:

Franklin), the name usually given to apparatus designed to protect buildings or See also:

SHIPS

ships from the destructive effects of lightning (Fr. paratonnerre, Ger. Blitzableiter). The upper regions of the See also:

ATMOSPHERE (Gr. fir µ6r, vapour; orkaipa, a sphere)

atmosphere being at a different See also:

electrical potential from the See also:

earth, the thick dense clouds which are the usual prelude to a See also:

THUNDER

thunder See also:

storm serve to conduct the See also:

ELECTRICITY

electricity of the upper See also:

air down towards the earth, and an electrical See also:

DISCHARGE (adapted from the O. Fr. discharge, modern decharge, from a med. Lat. discargare, to unload, dis- and earn care, to load, cf. " charge ")

discharge takes See also:

PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place across the air space when the pressure is sufficient. Lightning discharges were distinguished by See also:

Sir See also:

Oliver See also:

Lodge into two distinct types—the A and the B flashes. The A flash is of the See also:

SIMPLE

simple type which arises when an electrically charged See also:

CLOUD (from the same root, if not the same word, as " clod," a word common in various forms to Teutonic languages for a mass or lump; it is first applied in the usual sense in the late 13th century; the Anglo-Saxon chid is only used in the sense of " a ma

cloud approaches the earth without an intermediate cloud intervening. In the second type B, where another cloud intervenes between the cloud carrying the See also:

PRIMARY

primary See also:

charge and the earth, the two clouds practically See also:

FORM (Lat. forma)

form a See also:

CONDENSER

condenser; and when a discharge from the first takes place into the second the See also:

FREE

free charge on the earth See also:

side of the See also:

LOWER

lower cloud is suddenly relieved, and the disruptive discharge II Testing meters. 8 1.24 Type o£ See also:

LAMP (from Gr. Xag ras, a torch, Xaµaav, to shine)

Lamp . Number Distance See also:

TOTAL

Total See also:

AVERAGE

Average c.p. Cost per c.p. of Lamps. apart (yds.) Cost. per Mile. per annum. Incandescent See also:

gas .

2,137 8o £7,062 839 i5.86d. Incandescent electric 90 66 288 1,373 13'71 Electric arcs 428 65 7,212 10,537 11.32 from the latter to earth takes such an erratic course that according to the Lightning See also:

RESEARCH (O. Fr. recerche, from recercher, re- and cercer, mod. chercher, to search; Late Lat. circare, to go round in a circle, to explore)

Research See also:

COMMITTEE (from commute, an Anglo-Fr. past participle of commettre, Lat. committere, to entrust; the modern Fr. equivalent comite is derived from the Eng.)

Committee " no See also:

SERIES (a Latin word from serere, to join)

series of lightning conductors of the hitherto recognized type suffice to protect the See also:

BUILDING

building." In See also:

Germany two kinds of lightning stroke have been recognized, one as " ziindenden " (causing See also:

FIRE (in O. Eng. f j'r; the word is common to West German languages, cf. Dutch vuur, Ger. Feuer; the pre-Teutonic form is seen in Sanskrit pu, pavaka, and Gr. irup; the ultimate origin is usually taken to be a root meaning to purify, cf. Lat. purus)

fire), analogous to the B flash, the other as " kalten " (not causing fire), the See also:

ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary A discharge. The destructive effect of the former was noticed in 1884 by A. See also:

Parnell, who quoted instances of damage due to See also:

MECHANICAL

mechanical force, which he stated in many cases took place in a more or less upward direction. The See also:

OBJECT

object of erecting a number of pointed rods to form a lightning conductor is to produce a glow or See also:

brush discharge and thus neutralize or relieve the tension of the thunder-cloud. This, if the latter is of the A type, can be successfully accomplished, but sometimes the lightning flash takes place so suddenly that it cannot be prevented, however See also:

GREAT

great the number of points provided, there being such a See also:

STORE (from O. Fr. estor or estoire, Late Lat. staurum or instaurum, stock, provisions, supply, from the late use of instaurare, to provide, properly to construct, renew, restore)

store of See also:

ENERGY (from the Gr. ivipyela; iv, in, ipyov, work)

energy in the descending cloud that they are unable to See also:

ward off the See also:

SHOCK, or COLLAPSE

shock. A B flash may ignore the points and strike some See also:

metal See also:

WORK

work in the vicinity; to avoid damage to the structure this must also be connected to the conductors. A single air terminal is of no more use than an inscribed sign-See also:

BOARD (O. Eng. bord)

board; besides multiplying the number of points, numerous paths, as well as interconnexions between the conductors, must be arranged to See also:

lead the discharge to the earth. The See also:

SYSTEM

system of pipes and gutters on a roof must be imitated; although a single See also:

RAIN (O.E. regn; the word is common to Teutonic languages, cf. Ger. Regen, Swed. and Dan. regn; it has been connected with Lat. rigare, to wet, Gr. 13pixeav)

rain-See also:

WATER

water See also:

PIPE

pipe would be sufficient to See also:

DEAL

deal with a summer shower, in practice pipes are used in sufficient number to carry off the greatest storm. Protected See also:

AREA

Area.—According to Lodge " there is no space near a rod which can be definitely styled an area of See also:

PROTECTION

protection, for it is possible to receive violent See also:

SPARKS, JARED (1789-1866)

sparks and shocks from the conductor itself, not to speak of the innumerable secondary discharges that are liable to occur in the See also:

wake of the See also:

main flash." The See also:

REPORT (O.Fr. report or raport, modern rapport, from O.Fr. reporter, mod. rap porter, Lat. reportare, to bring back, in poetical use only, of bringing back an account, news, &c.)

report of the Lightning Research Committee contains many examples of buildings struck in the so-called " protected area." Material for Conductors.—Franklin's See also:

ORIGINAL

original rods (1752) were made of See also:

IRON [symbol Fe, atomic weight 55.85 (0=16)]

iron, and this metal is still employed throughout the See also:

CONTINENT (from Lat. continere, "to hold together "; hence " connected," " continuous ")

continent of See also:

EUROPE

Europe and in the See also:

UNITED

United States. See also:

BRITISH

British architects, who objected to the unsightliness of the rods, eventually specified See also:

COPPER (symbol Cu, atomic weight 63.1, H=1, or 63.6, O = 16)

copper tape, which is generally run See also:

ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

round the See also:

sharp angles of a building in such a manner as to increase the chances of the lightning being diverted from the conductor. The popular See also:

IDEA (Gr. Ibia, connected with i&eiv, to see; cf. Lat. species from specere, to look at)

idea is that to secure the greatest protection a rod of the largest area should be erected, whereas a single large conductor is far inferior to a number of smaller ones and copper as a material is not so suitable for the purpose as iron.

A copper rod allows the discharge to pass too quickly and produces a violent shock, whereas iron offers more impedance and allows the flash to leak away by damping down the oscillations. Thus there is less See also:

CHANCE (through the O. Fr. cheance, from the Late Lat. cadentia, things happening, from cadere, to fall out, happen; cf. " case ")

chance of a side flash from an iron than from a copper conductor. Causes of Failure.—A number of failures of conductors were noticed in the 1905 report of the Lightning Research Committee. One cause was the insufficient number of conductors and earth connexions; another was the See also:

ABSENCE (Lat. absentia)

absence of any system for connecting the metallic portion of the buildings to the conductors. In some cases the main stroke was received, but damage occurred by side-flash to isolated parts of the roof. There were several examples of large metallic surfaces being charged with electricity, the greater See also:

PART

part of which was safely discharged, but enough followed unauthorized paths, such as a speaking-See also:

TUBE (Lat. tuba)

tube or electric See also:

bell wires, to cause damage. In one instance a flash struck the building at two points simultaneously; one portion followed the conductor, but the other went to earth See also:

JUMPING

jumping from a small See also:

FINIAL (a variant of " final "; Lat. finis, end)

finial to a greenhouse 30 ft. below. Construction of Conductors.—The See also:

general conclusions of the Lightning Research Committee agree with the See also:

INDEPENDENT

independent reports of similar investigators in Germany, See also:

Hungary and See also:

Holland. The following is a See also:

SUMMARY

summary of the suggestions made: The conductors may be of copper, or of soft iron protected bygalvanizing or coated with lead. A number of paths to earth must be provided; well-jointed rain-water pipes may be utilized. Every See also:

CHIMNEY (through the Fr. cheminee, from caminata, sc. camera, a Lat. derivative of caminus, an oven or furnace)

chimney stack or other prominence should have an air terminal. Conductors should run in the most See also:

DIRECT

direct manner from air to earth, and be kept away from the walls by holdfasts (fig.

1), in the manner shown by A (fig. 2); the usual method is seen in B (fig. 2), where the tape follows the See also:

CONTOUR

contour of the building and causes side flash. A building with a See also:

long roof should also be fitted with a See also:

HORIZONTAL

horizontal conductor along the See also:

ridge, and to this aigrettes (fig. 3) should be attached; a simpler method is to support the See also:

cable by holdfasts armed with a spike (fig. 4). See also:

JOINTS

Joints must be held together mechanically as well as electrically, and should be protected from the See also:

ACTION

action of the air. At See also:

Westminster See also:

Abbey the cables are spliced and inserted in a See also:

box which is filled with lead run in when molten. Earth Connexion.—A copper See also:

PLATE

plate not less than 3 sq. ft. in area may be used as an earth connexion if buried in permanently See also:

DAMP

damp ground. Instead of a plate there are advantages in using the tubular earth shown in fig. 5. The cable packed in See also:

CARBON (symbol C, atomic weight 12)

carbon descends to the bottom of the perforated tube which is driven into the ground, a connexion being made to the nearest rain-water pipe to secure the necessary moisture.

No further See also:

ATTENTION (from Lat. ad-tendo, await, expect; the condition of being " stretched " or " tense ")

attention is required. Plate earths should be tested every See also:

YEAR

year. The number of earths depends on the area of the building, but at least two should be provided. Insulators on the conductor are of no See also:

ADVANTAGE

advantage, and it is useless to gild or otherwise protect the points of the air-terminals. As heated air offers a See also:

GOOD, JOHN MASON (1764-1827)

good path for lightning (which is the See also:

REASON (Lat. ratio, through French raison)

reason why the See also:

KITCHEN (O.E. cycene; this and other cognate forms, such as Dutch keuken, Ger. Kiuche, Dan. kokken, Fr. cuisine, are formed from the Low Lat. cucina, Lat. coquina, coquere, to cook)

kitchen-chimney is often selected by the discharge), a number of points should be fixed to high chimneys and there should be at least two conductors to earth. All roof metals, such as finials, flashings, rain-water gutters, ventilating pipes, cowls and See also:

STOVE

stove pipes, should be connected to the system of conductors. The efficiency of the See also:

INSTALLATION

installation depends on the interconnexion of all metallic parts, also on the quality of the earth connexions. In the See also:

case ; Q,•;'i a ° .qor of magazines used for See also:

EXPLOSIVES

explosives, it is .: questionable whether the usual See also:

plan of FIG. 5.—Tubular Earth. erecting rods at the sides of the buildings is efficient. The only way to ensure safety is to enclose the See also:

MAGAZINE

magazine in iron; the on Roof. next best is to arrange the conductors so that they surround it like a See also:

BIRD

bird cage.

End of Article: LIGHTNING

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