| Show I DARK LG TNIl G A PigPhenmenon Exp1aine ly Professor Wood New York Tribune A mystery In regard to lightning flashes has at last beeh cleared up Within the lat few years a large number num-ber of photograph have been taken hi which the path of the thunderbolt appeared ap-peared a dark line Instead oC a brIght one The curiously meandering route I of the line as well a Its c cterlstc ramifications prove udmlstakabl3 that It represented lightning One suspicion that has been enter tamed is that the Intensjty of the light produced what IS called a reera on the photographic plate I L l a well I established fact that i an attempt is male to photograph the sun or I small part of the solar surface the lmaqe obtained will be black and not white I the time o exposur i not very brief Photographers have been get bothered to abbreviate the exposure ex-posure sufficiently to get a proper picture pic-ture ot the sun I was observed however how-ever that faint lightning flashes ca out dark In a photograph a well a bright ones and thus I was roved that intensity was not the true ex plantion or the puzzling phenomenon he appearance of dark and brIght flashes on the same plate led to aUtte speculation as to the possibility of there being two kinds of lightning a I dark kind and 1 bright But no expert In electricity could be found who would I sanction such a notion and lt as impossible I Im-possible to obtain any evidence of such flashes actually having hen seen by anybody Indeed It Is hard to conceive of such a thin as a dark flash Professor n W Wood qf Madlsm Wis has ascertained that the brevity of a lightning flash has somethIng to do with the observed effect He tried a number of laboratory experiments like those of Mr Lk el but tried other means of lulnato than the spark The whole of a sensitive plate was expose to cd light for a second sec-ond or to and then 1porton of It was nvn In Tt si the fnln1 that the doubly exposed part sas affected twice a much as the rest of the plate There was no reversal here A much more rapid flash was ten tried An explosion of oxygen and hydrogen gases was brought about twice In succession and the same plate exposed to both flashes These flashes last about 112000 of a second But Professor Wood ale to Jet a reversal and thus wns le to conclude that the time was too lon Finally he arne a mach anim which would allow a beam of light from an electric arc to pass I through a slit that wrs opened for only 15000 of a second Then hc was able to reproduce the pheomentn or re verl every time The brevity of the flaSh then seem t1be another factor In the case I l rJ The mystery Is thus found to be a chemlcone I resides not in the skY but In thc sensitive film on the phQto graphic plate There Is nce such thing a dnrk lgtning What actually hap pent Ia 1 this The sensitizing materials are P31yz r to speak or rendered nLrosi ntreh Inoperative wherp the Imag of the flash fails upon the plate The ret ot the pate may then register I regs ter later flashes iud even stationary objects ike buldh1Hs but no such a ton can occur li the IrsnslUve streak made by th final flash Mr Locher has 5uggeted that In the thnderst2r season amateurs arrange ar-range to expose two cameras side by side directing the to the same qua tm the heavens Then after a particularly par-ticularly bright flash one instmit should be capped immediately while the plate In the other should be kept expoSe long enough to record one or two more flashes It anyone can get a dark flash for his first and only Image he Will upset 1r O1ttdens theory bout until someone doe w that hypothesis I will probably be generally aCCte |
