ELECTRICITY. 



421 



History, red spot, from the pores of which some drops of blood 

 Y"" ' oozed, without wounding the skin. The shoe on 

 the left foot was burst open ; and below the aperture 

 there was a blue mark on the foot, from which it is 

 probable that the electricity had issued. -Several red 

 and blue spots resembling leather shrunk by being 

 burnt, appeared on the left side, on the back, and 

 on other parts of the body. The stocking was entire 

 at the place where the shoe was burst, and the coat had 

 received no damage. The back of the engraver's coat, 

 however, was marked with several long and narrow 

 burnt stripes. Upon opening the body 24 hours after 

 the accident, the cranium and brain were uninjured ; 

 some extravasated blood appeared in the cavities below 

 the lungs, and in the lungs towards the back, which 

 were of a brownish-black colour. The throat, glands, 

 and the thin intestines, were all inflamed, but none of 

 the entrails were touched. The singed leather-coloured 

 spots merely penetrated the skin ; and 48 hours after 

 death, the body was completely corrupted. It is a. cu- 

 rious circumstance, that Professor Richman had in his 

 left coat pocket 70 rubles of silver, which were not in 

 the least degree affected. 



elavaT ^ ur coun tryman, Mr Delaval, a member of the 



pen. Royal Society, contributed considerably to the progress 

 enu. of electricity. He found that the calces of metals, such 

 as ceruse, lead ashes, minium, calx of antimony, &c. 

 are all non-conductors, although metals themselves are 

 the most perfect conductors. Animal and vegetable 

 solids also, when reduced to ashes, were likewise non- 

 conductors. A piece of Portland .stone, which conducted 

 perfectly well, became a non-conductor when powdered, 

 exactly like the oxides of metals; and after making si- 

 milar experiments with pounded alum, and gum arabic, 

 Mr Delaval believed that all bodies that can be pul- 

 verised in the mortar will have the same property. 

 Having formed some of the Portland stone, (granular 

 limestone) into plates nearly as thin as window-glass, 

 he heated them to a proper degree, and coated them on 

 both sides with metal, in order to perform the Leyden 

 experiment. When the heat was great enough to singe 

 paper, the stone conducts as perfectly as when cold. 

 Upon cooling, it logins to lose its conducting power 

 and afford small shocks, which increase in intensity for 

 ten minutes, and then continue the same for fifteen 

 minutes. The shocks then became weaker as the stone 

 cooled, and completely ceased a little while before the 

 stone was cold. The same result was obtained with 

 tobacco pipes. These results were attributed, by Mr 

 Canton, with great reason, to the moisture contained in 

 the Portland stone and the tobacco pipe. When they 

 are heated, the moisture is expelled, and the conduct- 

 ing power destroyed; and when they begin to cool, the 

 moisture is absorbed, and the conducting power re- 

 stored. Mr Delaval made some curious experiments on 

 calcareous sjwr. After being rubbed when the heat of 

 the air is moderate, it .shows wtak signs of electricity. 

 When the heat is a little greater than that of the hand, 

 it destroys completely its electric power, and by cool- 

 ing the electric power is a^ain revived. He plunged 

 the same crystal into a vessel of quicksilver surround- 

 ed by ice. After remaining two hours in cold water, 

 he took it out with a pair of ton^s, and upon again 

 rubbing it, it showed more electricity than it had done 

 formerly. He also found gome pieces of calcareous 

 spar that did not possess' this property. This circum- 

 stance will accou7it for the failure of Mr Bergman in 

 trying to repeat these exj>eriments of Delaval. 



Mr Benjamin Wilson made a number of experiments 



on electricity, which he published in 1750, in a trea- 

 tise on-that subject, and in several papers in the Philo- 

 sophical Transactions. He was unfortunately one of 

 those individuals who opposed, with such obstinacy, the 

 use of pointed conductors for thunder-rods, and was 

 the means of introducing into the Royal Society those 

 animosities and dissensions so fatal to the character and 

 interests of science. The electrical properties of the 

 tourmalin had been lately announced in the Memoirs 

 of the Academy of Berlin, by M. .ZEpinus, who found 

 that when this mineral was moderately warmed, it ex- 

 hibited a plus electricity on one side, and a negative 

 electricity on the other. The Duke de Noya, who 

 wrote upon this subject, maintains, that the two sides 

 are electrified plus, and one of them more strongly than 

 the other. In this state of the subject, it was taken up 

 by Mr Wilson, who made his experiments on a specimen 

 belonging to Dr Heberden, which weighed about 120 

 grains. The general result of these experiments was, 

 that the tourmalin suffers the electric fluid to pass 

 through it only in one direction, having, as it were, 

 two electrical poles ; that there are three different me- 

 thods of heating the tourmalin, which produce diffe- 

 rent electric appearances; that different degrees of heat 

 give different phenomena ; and that friction has the 

 same effect upon it as upon glass. Mr Wilson found 

 that a number of other crystallised minerals of a red and 

 orange colour, and having the hardness of topaz, pos- 

 sessed the same electrical quality as the tourmalin. 

 Dr Thomson, however, has remarked, that these must 

 have been varieties of tourmalin, which the imperfect 

 state of mineralogy did not enable Mr Wilson to recog- 

 nize. Mr Wilson also found, that when two electrics 

 are rubbed together, the one is always electrified po- 

 sitively and the other negatively, the harder of the two 

 having generally acquired the positive electricity. 



About this time a number of curious experiments 

 were made by Mr Symmer, on the electricity of stock- 

 ings of different kinds. His papers were published in 

 the Philosophical Transactions for 1759, and relate to 

 four subjects : 1. On the electricity of the human body, 

 and the animal substances silk and wool. 2. On the 

 electricity of black and white silk. 3. On electrical 

 cohesion. 4. On two distinct powers in electricity. 

 Mr Symmer had frequently observed, that, on pulling 

 off his stockings in the evening, they emitted a crack- 

 ling noise, and even gave sparks of fire in the dark. He 

 immediately conjectured that these phenomena were 

 electrical, and commenced a series of experiments on 

 the subject. He found the electricity very powerful 

 when a silk and worsted stocking were on one leg, and 

 it was of no consequence which of them was upper- 

 most. When the stockings are thus excited, they ap- 

 pear more or less inflated, discharge an electrical wind 

 felt by the bare leg, attract or repel another stocking 

 visibly, and by being touched, emit or receive electri- 

 cal fire. The best way of taking off the stockings is 

 to put the hand between the leg and the stockings, and 

 to push them off together. They must then be pulled 

 asunder, and will exhibit signs of electricity. When 

 tlie .stockings were both of the same colour, they pro- 

 duced no electricity, so tliat it was always necessary to 

 have one of them black and the other white. Having 

 worn a pair of 1 jnck silk stockings on his leg for ten 

 minutes, he found them so highly inflated when taken 

 off, that each of them exhibited the entire shape of the 

 leg, and rushed together at the distance of one foot and 

 a half. All these effects are most powerful when the 

 stockings are either new., or newly washed. 



4 



History. 



Labours of 

 Mr Wilson. 

 Died 1788. 



Experi- 

 ments of 

 Symmer, 

 1T59. 

 Died 1768. 



