LECTURE ON ELECTRICITY.

New Zealand Times, Volume XXX, Issue 4534, 1 October 1875, Page 2

LECTURE ON ELECTRICITY.

An instructive lecture was delivered last night by Mr. H. F. Smith, telegraphic mechanician, in the Dixon-street schoolroom, before the Young Men’s Wesleyan Mutual Improvement Society. The subject was “Electricity,” illustrated by experiments. The Rev. W. Morley occupied the chair, and introduced the lecturer in a few preliminary remarks. The lecturer then said ; “ There is, perhaps, no branch of experimental philosophy which is so popular with persons of all classes and ages as electricity, for which this reason might be assigned : that it is a science the general laws of which are susceptible of pleasing demonstration, and its phenomena, from the striking and ocular manner in which they may be presented, are calculated to arrest the attention and become fixed on the mind more powerfully than those of any other science. It had been customary to speak of electricity as if it were a distinct and infinitely subtle fluid, capable of flowing as a current, or, on the other hand, as if the electric fluid were composed of two fluids, opposite in their nature, and capable of being separated from each other or held apart by certain processes, and which in' the act of re-com-bining produce those peculiar effects which are called electrical. These opinions are, however, mere theories, adopted for the purpose of simplifying the subject. Electricity is now generally considered to be a peculiar fluid which causes the atoms or ultimate particles of matter to alter their position with respect to each other, or, as it is technically termed, to become polarised. It is unnecessary, however, on this occasion to discuss those questions which are merely theoretical, or to consider those parts of the science of electricity which do not bear on the experiments about to be made. The student, in considering the various phenomena which come under his notice in the study of electricity, must necessarily form some theory in his own mind as to the nature of the element with which he has to deal. It would be well for the student, until his views are matured, to regard electricity as a substance like water or gas, having a veritable existence, and although easily convertible into heat, yet in every respect indestructible. It would be better for him to dismiss from his mind the idea of the existence of two different kinds of electricity, and to regard the earth as a vast reservoir, highly charged with only one kind of electricity (positive), and to view all electrical machines and batteries as mechanisms by which electricity is pumped out of the earth at one point and poured into it at another. When any object has less electricity than the adjacent earth, it is said to be charged negatively, and when it has an excess of electricity, it is said to be charged positively. lu either case the electric fluid would endeavor to flow from the earth to it, or from the object to the earth, until an equilibrium is established. Electrical phenomena are studied under three heads Statical electricity, current electricity, and magnetism. Statical electricity investigates the properties of the electric fluid when insulated. The electric fluid in this case is usually excited by friction. Hence statical electricity and frictional electricity are synonymous terms. Galvanism, or voltaic electricity, is that branch of the science which treats of the electric currents arising from chemical action, more particularly that attending the dissolution of metals. This is sometimes called dynamical electricity, because it deals with the electric fluid while in motion,and is so distinguished from frictional electricity. Magnetism is the power which certain bodies called magnets have to attract iron. They are of two kinds, natural and artificial magnets. Natural maguats consist of the ora of iron, familiarly known as loadstones, first discovered, it is said, in Magnesia, in Asia Minor. Artificial magnets are for the most part straight or bent bars of hardened steel, magnetised by the action of other magnets, as that of the galvanic current. No substance appears to be indifferent to the influence of the magnet, though iron is the most affected by it. The influence of magnetic currents on the magnetic needle was discovered by Professor Oersted, in 1820 ; the electric magnet by Professor Ampere, in 1820 ; and the galvanic magnet by Professor Schweiggen, in 1820.” The lecturer then went through a most interesting series of experiments elucidatory of the science of electricity as applied to telegraphy. He then demonstrated the great pactile power of the electric magnet, and exhibited an admirable piece of mechanism, which (influenced by a magnetic current) might be dumped between two bales of wool in a ship’s hold, and' being connected with the captain’s cabin, would apprise him of the increase in the temperature of the hold above a given point, by the ringing of a bell, which would continue until the heat decreased. He then made experiment with the electric light, which formed so efficient a beacon to mariners in foggy weather. The lecturer then passed the electric current through a series of vacuum tubes, one containing pure hydrogen, emitting a beautiful purple hue, while one containing oxygen gas showed films of silver light. Other tubes were also subjected to the action of the electric current —one containing nitrogen- gas giving out needle points of light, while a double branch tube showed on one tube a pale green and on the other a white light. A globular tube similarly acted on produced spiral rays of light, which were very pleasing. The next experiment illustrated the action of the torpedo. The following metals, amongst others, were then put under the action of the electric current, and emitted the hues placed after them Platinum, blue; brass,a bright purple; pieces of steel, a pale blue ; gold, a brilliant pde blue; lead, a bright purple ; pure zinc, a rich purple; steal filings, a bright pale blue ; copper, a bright green ; magnesia pale green ; sbeet-tiu, a bright violet. At the invitation of the lecturer several ladies and gentlemen formed a circle, and an electric shock was made to pass, much to the amusement of the spectators. A vote of thanks was accorded unanimously to Mr. Smith for his most interesting and instructive lecture and illustrative experiments.