The discussion on Mr. Carruther's paper on “Volcanic Action regarded as due to the Retardation of the Earth's Rotation” (See Transactions, page 352) then took place.
Mr. Irvine contended that—
Mr. Carruthers' hypothesis was based on an assumption, a mere deduction, à priori, that the earth had undergone a retardation in the rate of its motion on its polar axis, and that there may be other causes at work tending to increase its rate of rotation. Mr. Carruthers advanced no observations to prove his assumption.
Granting a retardation of rotation, and also that the earth is a solid mass, then that the result of retardation would not be an elongation of the polar axis, caused by pressure from the equator on the internal mass; but, on the contrary, a flood of water inundating the polar regions, and flowing from the equator to the
poles. The central fire theory is based on observed facts. He agreed with Mr. Mallett's observations, and places the depth at which rocks would become molten at from twenty to thirty miles from the surface. He is supported by the writings of Sir J. Herschel, 1866.
Mr. Carruthers quoted “astronomers and mathematicians,” but did not give their names. Mr. Irvine considered that the central fire theory completely accounts for all phenomena connected with earthquakes and volcanoes, and is in no way disproved by Mr. Carruthers. He thought that Mr. Carruthers' hypothesis fails when applied to the moon, and does not account for the extinct voclanoes and evidence of earthquake action observed there. The central fire theory agrees with Le Placis' nebular hypothesis, and fully accounts for the presence of volcanic action in all cosmical bodies.
Mr. Crawford remarked that, according to Burton, the temperature in the mines at Brazil did not increase at the same rate as in mines in other parts of the world.
Mr. Carruthers, in reply, stated he had brought no proofs that the earth's rotation was retarded, as he had taken the fact for granted. The tides must cause or tend to cause such retardation, and the astronomers had calculated the amount of it to be that stated in the paper. He had not considered it necessary to raise the question. The effect of any retardation would be, as stated by Mr. Irvine, to heap up the water of the ocean at the poles, and this would, in proportion to the specific gravity of water, as compared with that of earth, counteract the tendency of the crust to break. He thought it unnecessary to calculate to what extent this counteracting tendency had acted, as we know that the ocean is not heaped up at the poles, while the age of the earth is so great that a very large amount of elongation of the polar axis must have taken place on account of the retardation of the rotation. The only fact on which the central fire theory was founded was that in mines in Western Europe the heat always increased with the depth below the surfaces. As Mr. Crawford stated, in Brazil this was not the case, and even in Europe the increase of heat varies so much that it cannot be due to any cosmical cause. At Rotomahana it increases 100£ in six inches. Is this a fair measure of the increase of heat at this point as we approach the centre of the earth? Yet it is on similar facts that the central fire theory rests. Mr. Carruthers contended that the increase of heat at Rotomahana and elsewhere is due to the same cause, namely, volcanic action. If there really is such a great heat in the inner parts, they cannot be formed of any material similar to that of the surface rocks, as is shown by the specific gravity of the earth. As to the fact that the moon is mountainous, although its velocity of rotation is small, this
does not disprove the hypothesis. The moon has had a greater velocity of rotation than it has now, and has lost it owing to the earth's attraction; the energy of motion would there, as here, take the form of volcanic energy. At the same time the paper did not pretend to explain volcanic action in the moon. There is there a tide of 127 feet, which must have a great influence on the solid crust, although it is perhaps doubtful whether any amount of tide would cause volcanoes. The velocity with which molecular motion is transmitted through stone is greater than the velocity of rotation, and the heat generated by any bending of the crust which may take place would be spread over the whole crust, and not localised.
Mr. Travers read a paper entitled, “Notes on the Extinction of the Moa.” (See Transactions, page 58).
The Hon. Mr. Mantell said that Mr. Travers' paper was one of the most interesting on the subject of Moas that he had heard, and he would move, as the hour was late, that the discussion of the paper be postponed until next meeting, in order that members might have an opportunity of considering the matter. This was agreed to, and the meeting adjourned.