501 



ELECTRICITY. 



Slate clay, Srrkj, and luminous, but loses itab*orbent power ns it becomes bituminous. 1 



Slites, Sparks, and absorbed electric li^ht f'n>in the explosion. 



Hone stone, (iexxl spark, ami phocphoric by tin- c\plosion. " *~Y~**" 



Fullers' earth, ( !<>od bright spark, but slightly luminous. I \i>cri- 



^eddle, ' s>0 s | wrk . b llt purple stream, attended with n very sharp hissing noise. mc " u "* 



; . t . Armenian bole, Ramified spark. It is not luminous l>y the explosion. 



Basalt, Sparks radiated upon its surface, but not minified. 



Bricks and tiles, Small purple sparks of a bright red colour, slightly luminous. 



(Queen's ware, Good spark, flame-coloured,and radiated upon its surf ace, but not phosphoric. 



Ditto fractured, The unglazed surface gives a purple spark, and is luminous by tin explosion. 



Siliceous Genus. 



Rock crystals, Light, first red, and then white, t Singer); all phosphoric, (fitrimshire). 



Quartz, Phosphoric, with a dull white light; a purple stream instead of a spark. 



Flints, Small purple spark. Not so luminous as quartz. 



Lapis lazuli, Affords very good sparks, and is luminous by the shock, 



Agates, felspars, jaspers, Scots pebbles, Luminous by the explosion, and gave hissing purple sparks. 



1'urjili \ries and granites Hissing purple sparks, and luminous by the shock. 



Pudding stones, Similar hissing sparks. Oval pebbles more luminous than the sand. 



^. f Good sparks from the arborescent parts, but only a hissing stream from 



I the stone iu*clt', which is slightly luminous by the shock. 



Pumice stone Hissing stream in some parts, and good sparks in others, slightly luminous. 



Different kinds of glass, Neither give a spark nor are luminous. 



Slronlian Genus. 



Native carbonate of strontites, .... Only a hissing purple stream, but very luminous by the explosion. 



Combustibles. 



Roll brimstone, Gives no spark, and is scarcely luminous by the shock. 



Flowers of sulphur, Are not phosphoric. 



Phosphorus, Inflames both by the spark and shock. 



Charcoal, Some kinds afford good sparks, and are phosphoric, and some not. 



, , i c j i i i C Gives sparks, beautifully variegated, in minute spangles, radiated upon 

 Cannel coal and Sunderland coal, . | ^ , . but j jg pl ^ sphoric 



Hard and dry peat, Gives a very good spark, but is scarcely luminous. 



j U vi i . e f Gives no sparks, but the fluid spreads uniformly and silently over its whole 



Hard and brittle b.tumen, from I surface g ^ e]ectric } .^ m an exhaus ^ ed receivcr ; it is i uminous 



DerbyslHre, . . J by ^ sh ock. 



Elastic bitumen from Derbyshire, . . Is also luminous by the shock. 



(Give the same phenomena as bitumen, but are not luminous by the ex- 

 Jet and asphaltum, | plosion 



Amber, Gives no sparks, but is phosphorescent, particularly fat amber. 



Plumbago, Gives good sparks, and is not phosphoric. 



F.Bccts of 

 electricity 

 en colours. 



nUcoveritf 

 of Sir II. 

 Davy. 



Mr Skrimshire was not able to discover any phos- 

 phorescent appearances, either in the metallic ores or 

 oxides, or in the metals themselves. 



M. Cavallo found, that the colours of vermilion, car- 

 mine, verdigrise, white and red lead, were altered by 

 the electric shock ; but that orpiment, gamboge, sap 

 green, red ink, ultramarine, Prussian blue, and a few 

 other compounds of the above, were not altered. 



We have avoided in the present Section giving any 

 account of the brilliant electro-chemical researches of 

 Sir Humphry Davy, as we propose to give a full ac- 

 count of his splendid discoveries in our article GALVAN- 

 ISM. 



For farther information on this subject, see Frank- 

 lin's Letters, p. 90 ; Beccaria, EUttlricumo Artificial*, 

 p. 117, and Letlere dell' Ellettricismo, p. 282 ; Brooke's 

 Miscellaueoiis E*f>erime nls ; Cuthbertson's Practical 

 Electricity, p. Ibl 197; Nicholson's Journal, 4to. 

 \ol ii. p. 525, and vol. v. p. 136; Warltire, in Priest- 

 ley's Eifjeriments on Air, vol. iii. ; Van Troostwyk and 

 Deiman, Journal de Physique, Nov. 1789 ; Cavendish, 

 Phil. '[rant. 1784, vol. bxiv. p. 119; Id. 1785, vol. 

 Ixxv. p. S73 ; Id. 1788, vol. Ixxviii. p. 2(i ; Van Ma- 

 rum, Premiere Continuation des Experiences Faitcs par 

 le Moyentde la Machine Electriyue Tvykrienne, p. 1W; 



Kienmayer, in Rozier's Journal, vol. xxxiii. page 101 ; 

 Pearson, Phil. Trans. 1797, vol. Ixxxvii. p. 142; AVol- 

 laston, Phil. Trans. 1801, vol. xci. p. 427 ; Priestley's 

 History of Electricity, p. 294, 312 ; Skrimshire, in M- 

 c/iolson's Journal, vol. xv. p. 281, vol. xvi. p. 101, and 

 vol. xix. p. 153; Singer's Elements of Electricity, part i. 

 chap. iii. ; and Cavallo's Electricity. 



SECT. III. On the Magnetic effects of Electricity. 



I N enumerating the points of resemblance between On the 

 lightning and electricity, Dr Franklin remarks, that they magnetic 

 have both the power not only of reversing the poles of effects of 

 magnets, but of destroying the magnetism altogether. c ' eftr ' l '''5 r - 

 By transmitting a shock of lour large jars through a fine 

 sewing needle, he gave it such a degree of polarity that 

 it readily traversed when laid on the surface of water. 

 If the needle lay east or west when it was struck, the end Franklin'* 

 which was entered by the electric shock jxiintetl north, txixri- 

 but if it lay north and south, the end which lay towards menu. 

 the north continued to point towards the north, whether 

 the shock entered at that end or at the other. He like- 

 wise found that the communicated polarity was strong- 

 est when the needle was struck lying north and .south. 

 and weakest when it lay east and west. In these expe- 



