COLLEGE LECTURES.

Globe, Volume XX, Issue 1410, 22 August 1878, Page 2

COLLEGE LECTURES.

FBICTIONAIi EXKCTEICITY.

The second of the course of experimental lectures on electricity and magnetism was delivered by Professor Bickerton last night in the lecture theatre of the College. The lecturer rommenotd punctually at 8 o'clock, the subject for the evening being " Prictional Electricity." He commenced by briefly reviewing the scope of the previous lecture, which dealt with the principles of magnetism, with an explanation of the properties of the magnet. Electricity, he observed, was first discovered in the substance called amber. Tn the old days it was thought that all knowledge was evolved out of men's brains, and hence there was a great deal of metaphysical reasoning Then ' Baoon and Galileo arose, and thereafter men began to ask questions of nature,'.ind thereby advancing scientific knowledge, which before had been only theoretical. By a series of familiar experiments the lecturer demonstrated, the properties of attrac. tiou and repulsion possessed by various substaucoß, such as paper, eealiug wax, guU&

percha, metal, vulcanite, and glass. Ele3tricity had been divided into two kinds, vitreous and resinous, but these were a misapplication of terms. Franklin had demontrated this by experiments, and had adopted in preference the terms positive and negative electricity, or plus and minus. For instance, vulcanite might be rubbed with cat's fur, which would form negative electricity, and when • rubbed with amalgamated silk would generate positive electricity. Substances divided themselves into two kindp, conductors and non-conductors of electricity. Metal was a conductor, and glass a nonconductor. This theory Professor Bickerton practically explained with the aid of the gold leaf electroscope. Dryness and moisture, he said, had a sensible effect in increasing and decreasing the conductivity of electricity in various substances that are either conductors or non-conductors. He next explained the principle of insulation, pointing out that when a substance is surrounded by non-conductors it is said to be insulated. The principle of charging the electroscope with electricity by induction was then shown, and also the method by which the electric fluid is distributed and discharged. The lecturer then elucidated the theory of the electrophorus, alternately charging and discharging it, and lighting the gas with an electric spark. The distribution of electricity was also shown by the use of the metallic disc and cone. The principle of the plate and cylindrical electrical machine was next explained, with experiments showing the opposing forces of attraction and repulsion on a bunch of pendant paper leaves, which alternately expanded or contracted as the electric current was applied or withdrawn. The principle of the lightning conductor was the next point for explanation, and by a very simple experiment the lecturer demonstrated the great necessity for miking complete contact with the earth to secure the advantages of this valuable application of science. The last part of the lecture was devoted to gome curious experiments with pith balls and figures, the electric current causing them, as it appeared, to be endowed with powers of volition, and, at the lecturer humorously observed, wan strongly suggestive of spiritualism. Professor Bickerton concluded by stating that the next lecture would exhaust the subject of frictional electricity, and the remainder of the course would be devoted to an explanation of what is known as Voltaio electricity as opposed to frictional. The latter, he explained, was more adapted to experimental than pradtical purposes, and might be regarded as only introductory to Voltaic electricity. The attendance was very good, and Professor Bickerton's explanation of che various electrical phenomena, with tho experiments he demonstrated them by, excited a great amount of interest.