aeroplanes and dirigibles of war-第37节

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the　legs　acting　as　the　support。　　A　length　of　shaft　is　then

slipped　into　sockets　at　the　inner　ends　of　the　motor　and　dynamo

shafts　respectively；　thus　coupling　them　directly；　while　the

current　is　transmitted　through　a　short　length　of　flexible　cable

to　the　instruments。　　The　mast　itself　is　made　in　lengths　of　about

four　feet；　which　are　slipped　together　in　the　manner　of　the

sections　of　a　fishing　rod；　and　erected；　being　supported　by　means

of　wire　guys。　　In　this　manner　an　antenna　from　40　to　50　feet　in

height　may　be　obtained。



The　feature　of　this　set　is　its　compactness；　the　equal　division　of

the　sections　of　the　installation；　and　the　celerity　with　which　the

station　may　be　set　up　and　dismantled　in　extremely　mountainous

country　such　as　the　Vosges；　where　it　is　even　difficult　for　a

pack…horse　to　climb　to　commanding　or　suitable　positions；　there　is

still　another　set　which　has　been　perfected　by　the　Marconi

Company。　　This　is　the　〃knapsack〃　set；　in　which　the　whole　of　the

installation；　necessarily　light；　small；　and　compact；　is　divided

among　four　men；　and　carried　in　the　manner　of　knapsacks　upon　their

backs。　　Although　necessarily　of　limited　radius；　such　an

installation　is　adequate　for　communication　within　the　restricted

range　of　air…craft。



Greater　difficulties　have　to　be　overcome　in　the　mounting　of　a

wireless　installation　upon　a　dirigible。　　When　the　Zeppelin　was

finally　accepted　by　the　German　Government；　the　military

authorities　emphasised　the　great　part　which　wireless　telegraphy

was　destined　to　play　in　connection　with　such　craft。　　But　have

these　anticipations　been　fulfilled？　　By　no　means；　as　a　little

reflection　will　suffice　to　prove。



In　the　first　place；　a　wireless　outfit　is　about　the　most　dangerous

piece　of　equipment　which　could　be　carried　by　such　a　craft　as　the

Zeppelin　unless　it　is　exceptionally　well　protected。　　As　is　well

known　the　rigidity　of　this　type　of　airship　is　dependent　upon　a

large　and　complicated　network　of　aluminium；　which　constitutes　the

frame。　　Such　a　huge　mass　of　metal　constitutes　an　excellent

collector　of　electricity　from　the　atmosphere；　it　becomes　charged

to　the　maximum　with　electricity。



In　this　manner　a　formidable　contributory　source　of　danger　to　the

airship　is　formed。　　In　fact；　this　was　the　reason　why　〃Z…IV〃

vanished　suddenly　in　smoke　and　flame　upon　falling　foul　of　the

branches　of　trees　during　its　descent。　　At　the　time　the　Zeppelin

was　a　highly　charged　electrical　machine　or　battery　as　it　were；

insulated　by　the　surrounding　air。　　Directly　the　airship　touched

the　trees　a　short　circuit　was　established；　and　the　resultant

spark　sufficed　to　fire　the　gas；　which　is　continuously　exuding

from　the　gas　bags。



After　this　accident　minute　calculations　were　made　and　it　was

ascertained　that　a　potential　difference　of　no　less　than　100；00

volts　existed　between　the　framework　of　the　dirigible　and　the

trees。　　This　tension　sufficed　to　produce　a　spark　4　inches　in

length。　　It　is　not　surprising　that　the　establishment　of　the

electric　equilibrium　by　contact　with　the　trees；　which　produced

such　a　spark　should　fire　the　hydrogen　inflation　charge。　　In　fact

the　heat　generated　was　so　intense　that　the　aluminium　metallic

framework　was　fused。　　The　measurements　which　were　made　proved

that　the　gas　was　consumed　within　15　seconds　and　the　envelope

destroyed　within　20　seconds。



As　a　result　of　this　disaster　endeavours　were　made　to　persuade

Count　Zeppelin　to　abandon　the　use　of　aluminium　for　the　framework

of　his　balloon　but　they　were　fruitless；　a　result　no　doubt　due　to

the　fact　that　the　inventor　of　the　airship　of　this　name　has　but　a

superficial　knowledge　of　the　various　sciences　which　bear　upon

aeronautics；　and　fully　illustrates　the　truth　of　the　old　adage

that　〃a　little　learning　is　a　dangerous　thing。〃　　Count　Zeppelin

continues　to　work　upon　his　original　lines；　but　the　danger　of　his

system　of　construction　was　not　lost　upon　another　German

investigator；　Professor　Schiitte；　who　forthwith　embarked　upon　the

construction　of　another　rigid　system；　similar　to　that　of

Zeppelin；　at　Lanz。　　In　this　vessel　aluminium　was　completely

abandoned　in　favour　of　a　framework　of　ash　and　poplar。



The　fact　that　the　aluminium　constituted　a　dangerous　collector　of

electricity　rendered　the　installation　of　wireless　upon　the

Zeppelin　not　only　perilous　but　difficult。　　Very　serious

disturbances　of　an　electrical　nature　were　set　up；　with　the　result

that　wireless　communication　between　the　travelling　dirigible　and

the　ground　below　was　rendered　extremely　uncertain。　　In　fact；　it

has　never　yet　been　possible　to　communicate　over　distances

exceeding　about　150　miles。　　Apart　from　this　defect；　the　danger　of

operating　the　wireless　is　obvious；　and　it　is　generally　believed

in　technical　circles　that　the　majority　of　the　Zeppelin　disasters

from　fire　have　been　directly　attributable　to　this；　especially

those　disasters　which　have　occurred　when　the　vessel　has　suddenly

exploded　before　coming　into　contact　with　terrestrial

obstructions。



In　the　later　vessels　of　this　type　the　wireless　installation　is

housed　in　a　well　insulated　compartment。　　This　insulation　has　been

carried；　to　an　extreme　degree；　which　indicates　that　at　last　the

authorities　have　recognised　the　serious　menace　that　wireless

offers　to　the　safety　of　the　craft；　with　the　result　that　every

protective　device　to　avoid　disaster　from　this　cause　has　been

freely　adopted。



The　fact　that　it　is　not　possible　to　maintain　cornmunication　over

a　distance　exceeding　some　20　miles　is　a　severe　handicap　to　the

progressive　development　of　wireless　telegraphy　in　this　field。　　It

is　a　totally　inadequate　radius　when　the　operations　of　the　present

war　are　borne　in　mind。　　A　round　journey　of　200；　or　even　more

miles　is　considered　a　mere　jaunt；　it　is　the　long　distance　flight

which　counts；　and　which　contributes　to　the　value　of　an　airman's

observations。　　The　general　impression　is　that　the　fighting　line

or　zone　comprises　merely　two　or　three　successive　stretches　of

trenches　and　other　defences；　representing　a　belt　five　miles　or　so

in　width；　but　this　is　a　fallacy。　　The　fighting　zone　is　at　least

20　miles　in　width；　that　is　to　say；　the　occupied　territory　in

which　vital　movements　take　place　represents　a　distance　of　20

miles　from　the　foremost　line　of　trenches　to　the　extreme　rear；

and　then　comes　the　secondary　zone；　which　may　be　a　further　10

miles　or　more　in　depth。　　Consequently　the　airman　must　fly　at

least　30　miles　in　a　bee…line　to　cover　the　transverse　belt　of　the

enemy's　field　of　operations。　　Upon　the　German　and　Russian　sides

this　zone　is　of　far　greater　depth；　ranging　up　to　50　miles　or　so


in　width。　　In　these　circumstances　the　difficulties　of　ethereal

communication　'twixt　air　and　earth　may　be　realised　under　the

present　limitations　of　radius　from　which　it　is　possible　to

transmit。



But　there　are　reasons　still　more　cogent　to　explain　why　wireless

telegraphy　has　not　been　used　upon　a　more　extensive　scale　during

the　present　campaign。　　Wireless　communication　is　not　secretive。　　

In　other　words；　its　messages　may　be　picked　up　by　friend　and　foe

alike　with　equal　facility。　　True；　the　messages　are　sent　in　code；

which　may　be　unintelligible　to　the　enemy。　　In　this　event　the

opponent　endeavours　to　render　the　communications　undecipherable

to　one　and　all　by　what　is　known　as　〃jambing。〃　That　is　to　say；　he

sends　out　an　aimless　string　of　signals　for　the　purpose　of

confusing　senders　and　receivers；　and　this　is　continued　without

cessation　and　at　a　rapid　rate。　　The　result　is　that　messages

become　blurred　and　undecipherable。



But　there　is　another　danger　attending　the　use　of　wireless　upon

the　battlefield。　　The　fact　that　the　stations　are　of　limited　range

is　well　known　to　the　opposing　forces；　and　they　are　equally　well

aware　of　the　fact　that　aerial　craft　cannot　communicate　over　long

distances。　　For　instance；　A　sends　his　airmen　aloft　and

conversation　begins　between　the　clouds　and　the　ground。　　Presently

the　receivers　of　B　begin　to　record　faint　signals。　　They　fluctuate

in　intensity；　but　within　a　few　seconds　B　gathers　that　an

aeroplane　is　aloft　and　communicating　with　its　base。　　By　the　aid

of　the　field　telephone　B　gets　into　touch　with　his　whole　string　of

wireless　stations　and　orders　a　keen　look…out　and　a　listening　ear

to　ascertain　whether　they　have　heard　the　same　signals。　　Some

report　that　the　signals　are　quite　distinct　and　growing　louder；

while　others　declare　that　the　signals　are　growing　fainter　and

intermittent。　　In　this　manner　B　is　able　to　deduce　in　which

direction　the　aeroplane　is　flying。　　Thus　if　those　to　the　east

report　that　signals　are　growing　stronger；　while　the　stations　on

the　west　state　that　they　are　diminishing；　it　is　obvious　that　the

aeroplane　is　flying　west　to　east；　and　vice　versa　when　the　west

hears　more　plainly　at　the　expense　of　the　east。　　If；　however；　both

should　report　that　signals　are　growing　stronger；　then　it　is

obvious　that　the　aircraft　is　advancing　directly　towards　them。



It　was