MOTION MOUNTAIN

liquid electricity, invisible fields and maximum speed 19
Ref. 3
Ref. 4
How can one make lightning?
F I G U R E 5 Lightning: a picture taken
with a moving camera, showing its
multiple strokes (© Steven Horsburgh).
Everybodyhasseenalightning flashorhasobservedtheeffectitcan have onstriking a
tree.Obviouslylightningisamovingphenomenon.PhotographssuchasthatofFigure5
showthatthetipofalightningflashadvancewithanaveragespeedofaround600 km/s.
Butwhatismoving?Tofindout,wehavetofindawayofmakinglightningforourselves.
In 1995, the car company Opel accidentally rediscovered an old and simple method of
achievingthis.
Opelengineershadinadvertentlybuiltasparkgeneratingmechanismintotheircars;
whenfilling thepetroltank, sparksweregenerated, whichsometimesleadtotheexplosionofthefuelatthepetrolstation.
Opelhadtorecall 2million vehicles.
Whathadtheengineersdonewrong?Theyhadunwittinglycopiedtheconditionsfor
a electrical device which anyone can build at home and which was originally invented
by William Thomson:*theKelvingenerator. Repeating his experiment today, we would
take two water taps, four empty bean or coffee cans, of which two have been openedat
bothsides, somenylon ropeand somemetal wire. Putting thisall togetheras shownin
Figure 6, and letting the water flow, we find a strange effect: large sparks periodically
jump between the two copper wires at the point where they are nearest to each other,
*William Thomson(b.1824Belfast,d.1907Largs),importantphysicistandprofessoratGlasgowUniversity.
He worked on the determination of the age of the Earth, showing that it wasmuch olderthan 6000years,
asseveralsectsbelieved,butalso(falsely)maintainedthattheEarthwasmuchyoungerthangeologistsand
Darwin (correctly) haddeduced.He stronglyinfluenced the development ofthe theory of magnetismand
electricity, the description oftheaether, andthermodynamics. Hepropagated theuseof theterm ‘energy’
asitisusedtoday,insteadoftheconfusingolderterms.Hewasoneofthelastscientiststopropagatemechanical
analogies for the explanation of phenomena, and thus strongly opposed Maxwell’s description of
electromagnetism. It was mainly for this reason that he did not receive a Nobel Prize. He was also one of
themindsbehindthelayingofthefirsttransatlantic telegraphiccable.Victorianandreligioustohisbones,
whenhewasknighted,hechosethenameofasmallbrooknearhishomeashisnewname;thushebecame
BaronKelvinofLargs. Thereforethe unitoftemperature obtained itsnamefromasmall Scottishriver.
Motion Mountain – The Adventure of Physics copyright © Christoph Schiller June 1990–November 2015 free pdf file available at www.motionmountain.net