The following is a short abstract of a lecture recently delivered by Faraday before the Royal Institution, London, and taken iron) the " London Expositer :"— The branch of the subject to which he directed attention in this introductory lecture, was the different means by which what is called static electricity may be excited, the term "static" being applied to distinguish that condition of electric force which is excited by friction on any insulated medium, from the electricity which is developed in a current state by voltaic action. The profe sor strenuously endeavored, in the first place, to impress on the minds of his auditors the great Importance and the extraordinory character pi the torce called into action by merely rub-tMg a glass rod with a piece of silk ; that force being sufficient, when operating on light bodies, to overcome the attraction of the earth. Several experiments were exhibited to show the excitement of electricity by the least possible friction ; among which the most curious was the divergence of the gold leaves of an electrometer by the movement ot Professor Faraday's feet on the carpet whilst lie touched the top of the instrument, I With a view torprwerttact" the bodies calletf* electrics do not derive the power of exciting electricity from similarity of their constituent particles, the two highly electrical substances, gutta percha and collodion, or gun cotton, were adduced, and by the different results of their combustion, the opposite characters of their elements were exhibited. It has been generally supposed that in the excitement of electricity by friction, it is "necessary that the rubber should be ot a different material from the electric ; but that this is not an essential condition was illustrated by the following experiment:—Two strip of dried flannel were rubbed against each other transversely the assistant holding one ot the strips tightly stretched whilst Professor Faraday rubbed the other briskly across it, and on applying the latter to the electrometer, the leaves diverged. Another experiment exhibited in a very striking manner the excitement of electricity that takes place whilst combing or brushing the hair when dry. A long lock of hair combed out with a tortoiseehell comb exhibited strong electrical indications by the hairs diverging separately from each other, and when the electricity was collected by an insulated metal plate, it served, after a few repetitions, to charge a small Leyden jar, by which gunpowder wus fired. The evolution of static electricity by evaporation was illustrated by pouring water into a small heated vessel placed on the electrometer. This mode ot excitiag electricity possesses peculiar interest from its being supposed to be the cause of the electrical phenomena of the atmosphere ; though whether this arises from mere change of state, or, as some philosophers imagine, from chemical action, remains a problem to be solved. The professor stated, however, as a circumstance lavorable to the latter hypothesis, that by no experiment yet devised has the excitement of electricity been rendered manifest by evaporation at the temperatures of the atmosphere. A small boiler was on the lecture table, for the purpose of showing the excitement of electricity during the emission of high pressure steam ; but this means of excitement, though apparently op-i posed to all others previously known, may be resolved into excitement by friction, caused by the forcible rubbing together of the particles of condensed steam as they issue from the jet. Professor Faraday did not, however, allude to the searching investigations and ingeniously contrived experiments by which he established this interesting fact ; a satisfactory evidence of which is, that when the injection pipe is heated, to prevent condensation, the excitement of electricity ceases. The last means of electrical excitement noticed was the unequal expansion of some crystalline bodies by heat ; which was illustrated by experiments with tourmelin, the substance in which this property was first observed.
This article was originally published with the title "Faraday on Static Electricity"