ELECTRICITY. 



upon the most accurate inquiry, found 

 that the vegetation of plants was in no 

 sensible decree either promoted or re- 

 tarded by common electricity. The 

 experiments of Van Marum, however, 

 in which be found that electricity in- 

 creased the evaporation of plants, ap- 

 pear to be entitled to some confidence ; 

 but still the effect observed, may, as he 

 himself remarks, have been occasioned 

 by the increased current of air from the 

 parts of the electrified leaves. His 

 observations on the influence of elec- 

 tricity on the sensitive plant, (Mimosa 

 pudica,) deserve also to be noticed. 

 The mere approach of an electrified 

 conductor, whether charged with posi- 

 tive or negative electricity, produced no 

 effect upon the plant ; but when sparks 

 were taken from it, the leaves collapsed, 

 just as they would have done by con- 

 cussions of a mechanical nature, and in 

 other respects the plant underwent no 

 change. In the Hedysarwn gyrans, a 

 plant remarkable for the continual ro- 

 tatory motions of its leaves, electricity 

 appeared to have no sensible influence 

 either in accelerating or retarding these 

 movements. 



(188.) The passage of shocks through 

 living plants immediately destroys the 

 vitality in the parts through which the 

 shock has been sent. It is, indeed, very 

 easy to kill plants by means of elec- 

 tricity. A very small shock, according 

 to Cavallo, sent through the stem of a 

 balsam, is sufficient to destroy it. A 

 few minutes after the passage of the 

 shock, the plant droops, the leaves and 

 branches become flaccid, and its life 

 ceases. A small Leyden phial, contain- 

 ing six or eight square inches of coated 

 surface, is generally sufficient for this 

 purpose, which may even be effected by 

 means of strong sparks from the prime 

 conductor of a large electrical machine. 

 The charge by which these destructive 

 effects are produced, is probably too 

 inconsiderable to burst the vessels of 

 the plant, or to occasion any material 

 derangement of, its organization ; and, 

 accordingly, it is not found, on minute 

 examination of a plant thus killed by 

 electricity, that either the internal ves- 

 sels or any other parts have sustained 

 perceptible injury. 



(189.) It appears from the experi- 

 ments of Mr. Achard, that the fermen- 

 tation of vegetable matter is accelerated 

 by electricity. 



(190.) The general conclusion de- 

 ducible from these inquiries' is, that 



feeble electricity exerts no perceptible 

 influence on cither animal or vegetable 

 life : but when transmitted in powerful 

 shocks, its destructive effects are simi- 

 lar to those which are produced by 

 lightning. 



CHAPTER XII. 

 Instruments adapted to collect weak 



Electricity. 



(191.) BEFORE we proceed to consider 

 the developement of electricity under 

 various circumstances, it will be proper 

 to give a description of several instru- 

 ments which have been contrived for 

 the purpose of collecting and exhibiting 

 weak degrees of electricity, that would 

 otherwise escape detection. All these 

 instruments derive their efficacy from 

 the principle of electric induction ; and 

 their mode of operation will be best 

 understood by previously directing our 

 attention to the electrophorus. 



(192.) The instrument termed the 

 Electrophorus was invented about the 

 year 1774 by Professor Volta, a name 

 which is associated with many im- 

 portant discoveries in the science of 

 electricity. It consists of three parts: 

 the essential part, which supplies the 

 electricity, being a cake of some electric 

 substance, (E,Jtg. 39,) such as sulphur, 



Fig, 39. 



gum lac, sealing-wax, pitch, or other 

 resinous composition ; this is melted 

 on a conducting plate S, called the 

 sole, w r hich is formed with a rim to 

 contain it, and the fluid then allowed 

 to congeal. The third part of the ap- 

 paratus consists of a circular metallic 

 plate C, provided with an insulating 

 handle fixed upon its upper surface. 

 This is called the cover ; and is some- 

 times made of wood, covered on all 

 sides with tin-foil well rounded at the 

 edges to prevent the dispersion of elec- 

 tricity. In order to bring the apparatus 

 into a state of activity, the surface of 

 the cake is excited by friction with fur 

 or flannel, and is thus rendered nega- 

 tively electrical. The cover, held by its 

 insulating handle, must now be placed 

 E 2 



