LIGHTNING.- 



tnay tiot give ele'cirie fire to, and air fuddenly condenfed re- 

 ceive e^ecTtr-c fire from, clo'.ids and vapours pafling through 

 it. Mr. Wilcke fiippofcs the air to contract its electricity, 

 in the fatne manner as fulphur and other fubllances do, when 

 thev are heated and cooled in contaft with various bodies. 

 Thus the air, being heated or cooled in the neighbourhood 

 of the earth, gives eleftricrty to the earth, or takes it from 

 it ; and the electrified air, being conveyed upv.'ards by va- 

 rious means, communicates its eleftricity to the clouds. 

 Others have queried, whether, fince thunder generally hap- 

 pens in a fiiltry ftate of the air, when it feems repleniflied 

 with feme fulphureous vapours, the eleftric matter then 

 in the clouds may not be generated by the fermentation 

 of fulphureous vapours with mineral or acid vapours in 

 the air. 



Dr. Franklin advifes perfons who are apprehenfive of 

 danger from ligiitninj, to fit in the middle of a room, pro- 

 vided it be not under a metal luflre fufpended by a chain, 

 fitting on one chair, and laying their feet on another. It 

 is ftill fafer, he fays, to bring two or three m'-tralfes, or 

 teds, in''o the middle of the room., and folding them double, 

 to place the chairs upon them, for as they are not fo good 

 conductors as the wall, the lightning wiU not choofe to pafs 

 through them : but the fafell place of all is in a hammock 

 hung with filken cords, at an equal diftance from all the 

 fides of a room. Dr. Prieftley obferves, th<?t the place of 

 niuft abfolute fafety mull be the. cellar, and efp^cially the 

 middle of it ; for when a perfon is lower than the furface 

 of the earth, the lightning m'.'ft ftrike it before it can 

 poffibly reach him. In the fields, the place of fafety is 

 within a few yards of a tree, but not quite near it. Never- 

 thelefs, S. Beccaria cautions perfons not to depend upon the 

 neighbourhood of a higher, or, in all cafes, a better con- 

 ductor than their own body ; fince, according to his re- 

 peated obfervations, the lightning by no means defccnds in 

 one undivided track ; but bodies of various kinds conduft 

 tteir {hare of it at the fame time, in proportion to their 

 quantity and condu6li:ig power. See on the fubjecl of this 

 article Frankhn's Letters ; Beccaria's Lettre dell' Elettri- 

 cifmo; Priellley's Hilloi-y, &c. of Eledtricity, paflim. Lord 

 Mahon (now earl Stanhope) obferves, that damage may be 

 done by lightning, not only by the main ftroke. and lateral 

 explofion, but likewife by that which he ca'ls the returning 

 flroke, that is, by the fudden violent return of that part of 

 the natural fhare of electricity (of any conducing body, or 

 of any combination of condu<3ing bodies) which had been 

 gradually expelled from fuch body or bodies refpedlively, 

 bv the fuperinduced elaftic eledlrical prefTure of a thunder 

 cloud's eleftrical atmofphere. See an account of his theory 

 and experiments, relating to this fubjeft, in his Piincipies 

 of EleClricity, &c. quarto, 1779. 



The author of the Philofopliy of Agriculture remarks, 

 that the blalls occafioncd by lightning are more frequent, 

 he believes, than is ufually f'lppofed ; as he is informed by 

 tbofe who purchafe extenfive woods, that very many trees, 

 on being fawed through, are found cracked and much in- 

 jured by lightning. He had latt year (1799) a (landard 

 app'e-tree and a tall apricot tree in full leaf, blafted at the 

 fame time by lightning, as was beheved. They both loll 

 all their leaves ; the apple-tree, nevcrthelefs, put out a new 

 foliage and recovered, and bore fruit this year ; but the 

 apricot, which was nailed to a high wall, never iliewed anv 

 returning life. Mr. Tull, he remarks, afcribes one injury 

 to the health of wheat plants, and frequently their death, 

 to lightning, the elfefts whereof may be obferved by the 

 blackifh parts or patches vilible in a field of wheat, efpecially 



in thofe years whicli have more thunder ftorms than ufuali 

 and adds, that againll this there is no remedy. The ereclion 

 of frequent metallic points could, as the dodor think?, alone 

 fecurc a garden or field from this misfortune ; which pro- 

 bably occurs more frequently on damp fituations than on 

 dry ones. 



He conceives, that the manner in which lightning deftroys 

 the life of vegetables may be fim.ilnr to that in which it de- 

 ftr.sys animal life ; which is, he fuppofes, by its great (li- 

 mulus, exhanding the fenfurial power in the violent aiflion it 

 occafions, and thus producing total inirritability to the com- 

 mon ftiinuh, which ought to excite the vital adlions of the 

 fyilem. It may alfo affecl vegetables in another way fimilar 

 to that, which probably alfo happens when their young 

 fucculent roots are frozen ; that is, by burlling their veflels, 

 as it paaos through them by its expanlive power; as haopens 

 to the large branches of fome trees, and to Hone buildino-s, 

 and other bad condutlors of electricity, when they are 

 ilruck with lightning. The expanfive power of ele&ricity 

 is not only (hewn by trees and towers being rent by light- 

 ning, but by the found which fucceeds the paifage of 

 it through air; fince a vacuum, or nearly a vacuum, in re- 

 fpecl to air, muft previoufly be made by the prefence of the 

 eleftric fluid : and the iides of this vacu'.:m rufhing together, 

 when the ilream has pafled, occafions the confequent vibra- 

 tions of the air, which conftitute found, whether in the 

 audible fpark of electricity, or the tremendous crafh of 

 thunder. Some ether efFecls on vegetables have been af- 

 cribed by writers to h,jhtning, but they have not yet been fa- 

 tisfac^orily proved. See Electricity. 



Lightning, Artificial. The phofphorus, when newly 

 made, gives a fort of artificial lightning vifible in the dark, 

 which would furprife thofe who are not ufed to fuch a phe- 

 nomenon : the ufual method of keeping this preparation is 

 under water, and if the corrufcations are defired to be feen 

 to the greateil advantage, the glafs in which it is kept (hould 

 be deep and cylindric, and not more than three-fourths filled 

 with water. The phofphorus put into this water will fend 

 up corrufcations at times, which will pierce through the in- 

 cumbent water, and expand themfelvcs with great bri^htnefs 

 in the empty upper part of the bottle. 



If we compare this artificial corrufcation to the real light- 

 ning, we (hail find, that as in this the fire pades unaltered 

 through the water, fo in that the flaihcs of lightning, which 

 co.ne at intervals, pafs uninterrupted through the moil denfe 

 clouds, and are not obftrucled by the heavicft ftorms of 

 rain, but like the beams of the fun, or anv other fire, pafs 

 uninterrupted through glafs and water. The feafm of the 

 weather, as well as the newnefs of the phofphorus, muft 

 concur to produce thefe flalhes' for they are as uncommon 

 in winter as lightning is, but in warm weather both are very 

 frequent. 



The flame of lightning is generally inoffenfive, aid does 

 not, except upon particular circumllances, fet fire to any 

 thing that it falls upon ; and, in like manner, the flafhings 

 of the phofphorus through the water will not burn tlie fleili, 

 nor even fire the mod combul'ible things ; though the phof- 

 phorus itfelf, like the lightning, under proper circum'lanees, 

 may be a very confuming and terrible fire. The warmth of 

 the air, or the immediate beams of the iun, will fet fire to 

 tiie condenfetl body of the phofphorus, and it then becomes 

 this terrible fire; and in the fame manner lightning, when con- 

 denfed and contracted, and wrapped up in 'a vehicle of air, 

 fo that it does not fo eafily diffufe itfelf through the yield- 

 ing ether, fe:s fire to trves, houfes, or whatever it conies 

 near. 



C 3 The 



