102 ME. SOLLY ON THE 



electricity, and the so-called vital energy of plants, remains still 

 involved in obscurity, and, in fact, constitutes one of tlie most 

 curious problems of vegetable physiology. These observations 

 of course apply only to growing plants ; the influence of free 

 electricity on tlie germination of seeds is quite a different con- 

 sideration : in electrifying seeds sown in earth, as in electrifying 

 those in Leyden jars, or wrapped up in tin foil previous to sowing 

 them, we really do not at all place them under the influence of 

 electricity, because we only electrify the outside surface of the 

 vessels in which tliey are placed, the surface of the soil, the coats 

 of the Leyden jar, and the outside of the tin foil in which tliey 

 are enclosed. 



Although it is the custom, in ordinary language, to speak of 

 negative and positive electricity, as tliough they were two dis- 

 tinct kinds of power, yet it must always be remembered that tlie 

 terms are merely relative, and that whenever we have any sub- 

 stance charged with the one, other substances in the neiglibour- 

 hood either are, or tend to become, in the opposite state ; which 

 conditions remain, until either by conduction or by other means the 

 mutual neutralization of the two is efifected. Tlius, under ordinary 

 circumstances, the surface of the earth and plants growing in it are 

 negative, whilst tlie air is positive ; and this condition is perpe- 

 tually being destroyed by the slow but continuous discharge which 

 is always taking place. Hence therefore the effects of frictional 

 electricity are divided into those of statical, and dynamical elec- 

 tricity, or those which are due to the mere proximity of masses of 

 matter in opposite electric states, and those which are due to the 

 act of neutralization of those opposite states. In the case of 

 galvanic electricity, or electricity of quantity, it is quite different ; 

 the effects produced by it are all those of dynamic electricity, 

 and, as the source which produces it continues, so the effects 

 themselves are continuous : galvanic electricity, or as it is some- 

 times termed current electricity, is always produced in a circuit, 

 which indeed is a necessary condition to its being evolved, and 

 to its producing those effects which are peculiar to it. Current 

 electricity may be excited in a circle of conducting matter by 

 chemical action occurring at one part of the circle, by inequality of 

 temperature, or by magnetic induction. Of the first case we 

 have an illustration in the ordinaiy voltaic battery, where elec- 

 tricity is evolved by the action of zinc upon water ; of the 

 second case we have an example in thermo-electric piles, where elec- 

 tricity is developed by the unequal temperature of the joints of a 

 compound series of two different metals ; and of the third we 

 have a beautiful illustration in the magneto-electric machines, 

 where a rapid succession of electric currents is produced by the 



