ELECTRICITY. 



487 



Descriptive the lightning is too powerful to permit the observer to 

 ertnoiy. carr y on the operation in safety, he connects the insu- 

 "~r~""' lated wire with the ground, and transmits the accumu- 

 lated electricity in silence to the earth. 



4th, During a driving fog, or a smart rain, the wire 

 is electrified almost as powerfully as during a thunder- 

 storm, and the electricity exhibits similar changes. 



5th, A weak positive electricity generally prevails 

 in cloudy weather. It often changes to negative when 

 rain falls ; but the positive electricity reappears when 

 the rain has ceased to fall. 

 6th, The positive electricity is more intense in clear 

 frosty weather than in a fine summer's day. 



States of the In the following Table, Mr Crosse has given the dif- 

 air in which ferent states of the air in which electricity appears, be- 

 iclt y ginning with those in which it is most powerful. 

 '"'. 1. During the occurrence of regular thunder clouds. 



2. 'A driving fog accompanied hy small rain. 



3. A fall of snow, or a brisk hail storm. 



4. A smart shower, especially in a hot day. 



5. Hot weather succeeding a series of wet days. 



6. Wet weather following a series of dry days. 



7. Clear frosty weather, either in the night or day. 



8. Clear warm summer weather. 

 9- A sky obscured by clouds. 



10. A mackerel back or mottled sky. 



11. Sultry weather, the sky covered with light hazy 

 clouds. 



12. A cold damp night. 



13. A peculiar state of .the atmosphere, which occurs 

 during north-easterly winds, and which is regarded as 

 particularly unhealthy, producing a sensation of dry- 

 ness and extreme cold, which is not indicated by a de- 

 pression of the thermometer. 



A rel number of experiments on atmospherical 

 electricity have been made by Mr Henley, Mr Hennet, 

 M. Achard, M. Cotte. M. Knnan, and various other au- 

 thors, but v.-e cannot find room to do any thing more 

 than refer to their re-pective works. 



For farther information on the subject, see Lemon- 

 nier, Mem. Acad. Par. 17.52, p. 233, 240, 2H. Abbe 

 Mazeas, Phil. Trant. 1 753, p. 377. Beccaria, AY/rf. 

 trici'a terrettre Atmnspherica, 1087, I't .-rq. Saus- 

 i'oi/nget duns let Alps, 8vo. edit. torn. iii. p. 

 315. Gardini, De in/luyt Llr.-lrii-itulis Almo- 

 sphcrricce, 50, 51. Ronayne, Phil. Trant. 1772, vol. 

 Ixii. p. 137. Henley, Phil. Trans. 1772, in remarks 

 at tbe end of Honayne's paper. Cavallo, Phil. Trains. 

 J77<>', p 4(>7, and 1777, p. 43. Achard, Mem. Acad. 

 lierliii, I 7M), p. Ik; /,/. 178(>, p. 13 I.ennet, P/iil. 

 Trans. 1787, p '^H. Head, Phil. Trans. 1791, p. 

 17!'-', p. 225. ; and Head's Summary View of the Elec- 

 tricity of the Ear'.h and Atmosphere, Lond. 1793. Cotte, 

 Mem. Acad. Par. 1772, p. 1. Erman, Journal de Phy- 



sique, vol. lix. p. 98; and Singer's Elements of Eleclri- Descriptive 

 city, p. 270, &c. Electricity 



2. On the Electricity of the Atmosphere as exhibited in 

 Thunder and Lightning. 



Although the existence of electricity in thunder On the elec- 

 storms is a modern discovery, yet there can be no doubt * ric ' tv o( tlle 

 that the ancients were well acquainted with numerous ^ exhibited 

 phenomena that had the same origin. { thunder 



Herodotus informs us, that the Thracians disarmed and light- 

 the heavens of its thunder, by throwing their arrows in nin B- 

 the air ; and that tile I lyperboreans produced the same 

 effect, by launching among the clouds darts armed with 

 points of iron. 



During the night before the battle which Posthmni- Electrical 

 us gained over the Sabines, the Roman javelins emitted phenomena 

 a light like torches ; and when Gylippus went to Syra- obit ' rvc(1 b >' 

 cine, he perceived a flame upon his spear.* According 

 to Procopius, the same appearance was seen in the war 

 which lk-li-,arius waged against the Vandals. t LivyJ 

 informs us, that Lucius Atreus having bought a javelin 

 for his son, who was about to be enrolled as a soldier, it 

 threw out names during two hours without being consu- 

 med by the lire. Similar facts nre mentioned in Plutarch || 

 and Pliny, the last of whom observed the phenomenon 

 himself. Ciesar informs us in his Commentaries, that 

 in the African war, after a tremendous storm, which 

 threw the Roman army into great disorder, the points 

 of the darts of a great number of the soldiers shone with 

 a spontaneous light. In the month of February, says 

 he, about the second watch of the night, there sudden- 

 ly arose a great cloud, followed by a dreadful storm of 

 hail, and in the same night the points of the darts of 

 the fifth legion appeared to be on fire. IT 



A very singular fact, analogous to those which we 

 have now stated, is mentioned by Bianchini. There had 

 existeil from time immemorial, in one of the bastions of 

 the castle of Duino, situated in the Frioul, on the banks 

 of the Adriatic Sea, a pointed iron rod standing in a ver- 

 tical position. In summer, when the weather had the 

 appearance of being stormy, the soldier who mounted 

 guard in this bastion, examined the iron rod, and pre- 

 sented to it the point of an iron halbert, which was al- 

 ways ready for this purpose, and whenever he percei- 

 ved that the iron rod gave sparks, or displayed a small 

 gerb of fire at its point, he rung a bell to give notice to 

 the country people who were working in the fields, or 

 to the fishermen who were at sea, that .stormy weather 

 was approaching. This custom was of great antiquity, 

 and is mentioned by Imperati in a letter dated 16'02. ** 



The production of electric light was no sooner disco- E ar ]y ;_ 

 vered by Dr VVall.tt than he noticed its resemblance to nions of Dr 

 lightning ; and the same remark was afterwards made Wall and 

 by Gray , + who imagined that both the thunder and the 



* " Gylippo Syracusas pctenti, visa eat Stella super ipsam lam-cam constitisse. In Romonorum castrii visa sunt ardcre piln, igni- 

 bus scilicet in ilia dclapsis : qui satpe, fulminum more, animalia fcrirc solent et arbusta, std si minorc ?i mittnntur, iefluunt tan. 

 turn et in-iiitnt. non feriunt nee vulnerant." Senec. ffatur. Quant, lib. U cap. 1. 



T Pru.Mpiiis De Bell. I'andalarum, lib. ii. cap. t. 



* Livy, lib. 43. 



|) In Siciliu militihus aliquot spirilla, in Sardinia mtiro circumcunti vigilias cquiti scipionem quern In manu tenuerat, ersissc, et lit- 

 tora crebris ignibus fulsiiwe." Plutarch De I'it. LytanJ. i 



" Vidi nocturnis railitum vigiliig inha-rerc pilis pro vallo fulgorcm eftigie ea - - - - hominum quoque capiti veepertinis horis magno 

 prsnafio, circurrifulftenu" Pliny Hat. A'nt. lib. ?. 



" Per id tempus fere Csesaris exercitui res accidit incrcdiliilis auclitu, ncmpc vigiliarum nignn confecto, circiter vigilia scrunda noc- 

 tis. nimbus cum taxea grandine fubito est cmirtus ingens; eadcm nocte legionis quinta- cacumina sua spontearii-rutit." Cars. C*om- 

 mtnt. de Iirll<, Africano, can. 6. This phenomenon was considered as electrical by M. de Cmirtlvton. Sec Mem. Actul. Par. ITfiZ. p. Id 



' Alluding to this custom of the inhabitanls of Duino, he observes, " Igne et hajta hi mire utunlur ad imbrcs, grandincs, procei- 

 lasqn .las, tempore presertim witivo." See Alcm. Jcoi far. 1 76+, p. 408, &C. 



+1- See the History of Electricity, p. 41?, col. t. 



X See the History of Electricity, p. 415, col. 1. 



