PROFESSOR TYNDALL ON HEAT.

New Zealand Times, Volume XXXII, Issue 5112, 11 August 1877, Page 2 (Supplement)

PROFESSOR TYNDALL ON HEAT.

(From the Spiritual Magazine?) On the-19th of April Professor Tyndall delivered the second of a course of lectures at the Royal Institution on " Heat." The professor affirmed that the equivalence of things —that was to say, that every effect must have its equivalent cause—was a great principle running throughout the physical universe. They never had creation of power or motion out of nothing. In the experiments with the thermo-electric pile and the galvanometer, it was the consumption of the heat of the warm face of the pile which produced the effect on the magnetic needle ; without that consumption of heat they did not get that effect. The lecturer then showed some interesting experiments to manifest the operation of a curious law namely, that when to natural gravity the presence of an electric or magnetic current was added, the resistance to be overcome was greater than would be required by gravity alone, and that the excess of strengtli which had to be exerted was converted into heat. This was illustrated with the eleetrophorous, but also in a number of other ways. Two heavy pieces of steel were placed a small distance apart, and between them a coil of copper wire was dropped on to a plate of tin below. Before the pieces of steel were magnetically connected, the lecturer counted two while the coil was falling ; when, the circuit was made he counted seven, showing that the coil was passing through an altered medium, and the resistance encountered was not magnetic attraction. The same thing was most effectively shown by the swinging of a pendulum between two masses of steel ; when there was no electric current the pendulum swung freely, but the raoment there was a circuit completed the pendulum was arrested. This was rendered still more obvious by the reflection of a beam of light on a screen from a mirror placed on the pendulum. In further illustration of the principle that the overcoming of the increased resistance generated heat, the lecturer caused a copper cylinder containing fusible metal to rotate with great rapidity in an open space between the two pieces of steel, electric communication having been set up. In a minute and a half the metal was poured out from the cylinder in a molten" state. The sensible increase of muscular force required to turn a large magneto-electric machine when the circuit was complete was compared by Professor Tyndall to the cutting of cheese or butter. The heat produced by the effort was transferred from his muscles, for no force introduced into the universe ever disappeared, so far as we knew. In another lecture he should, he said, have to inquire how the muscles, which by their exertion produced heat, did their work; and, goiDg further back, he should have to ask on what they had drawn in order to produce that power. Coming to chemical action, as a cause of intense heat: the lecturer showed an oxy-hydrogen flame, of the temperature of 4000 degrees centigrade. That intense heat, which pierced platinum, was caused by the violence with which the atoms of oxygen and hydrogen rushed- together, producing aqueous vapor. Rust was a slower combustion, and the reason why no heat was perceptible in that case was that the heat which was generated made its escape. , Professor Tyndall further showed the .effect of oxidation on a heated diamond placed in a vessel of oxygen gas, and said it was the impact of the atoms of oxygen in obedience to chemical affinity which produced the glow of the diamond. Before the chemical union of the oxygen with the. hydropen or carbon, those elements were in an atomic state ; afterunion they were in a molecular state.' The mental picture of the conduct of the atoms would correspond to. the ■physical illustration of two balls connected together by a spiral spring; when the balls were pushed together they recoiled, and quivered before coming to rest, fn chemical action producing heat, the atoms rushed together also, recoiled, and quivered, and it was not the rushing together, nor the recoil, but the quivering, that produced the phenomenon to which we gave the name of heat.