Lectures on electricity / by James Ferguson, F.R.S.

  • Ferguson, James, 1710-1776.
Date:
1825
Catalogue details

Licence: Public Domain Mark

Credit: Lectures on electricity / by James Ferguson, F.R.S. Source: Wellcome Collection.

    99/112 (page 93)
    EXPERIMENT II. Fill a flat porcelain dish with water, and strew over the surface a quantity of powdered resin : place two wires at the opposite sides of the dish at about five inches distance from each other : pass the charge of a jar from one wire to the other, and the resin in the track of the explosion will be inflamed. This experiment may be varied by strewing powdered resin upon a small quantity of cotton wool tied round the knob of the discharging rod ; when the discharge is made, the resin and cotton will be inflamed. The most remarkable effects of combustion produced by electricity are, the results of its action upon metal. These effects were first observed by Dr. Franklin : his experiments were followed by those of Mr. Kimmersly and Beccaria, and have since been investigated and ex- tended with great success by Mr. Brook, Dr. Van Marum, and Mr. Cuthbertson. Some of these effects have already been noticed by Ferguson, which it will not now be necessary to recapitulate. We therefore proceed to give those experiments which appear to throw most light upon this part of the subject. In all of the following experiments, Cuthbertson’s electrometer should be employed to regulate the charge. EXPERIMENT HI. Arrange two inches of pendulum wire in the circuit between the lower insulated ball of the electrometer and the external coating of the jar. Set the slider on the graduated arm of the electrometer to fifteen grains. The machine is then to be put in motion, and when the in- tensity of the charge exceeds the resistance of fifteen grains, the beam of the electrometer will descend, and the charge passing through the two inches of wire, will render it red hot and melt it into balls.