PHILOSOPHICAL SOCIETY.
A meeting of the members of this society was held on Saturday evening at the Provincial Hall. The vice-president of the society, W. T. L. Travers, Esq., F.L.S., occupied the chair. The minutes of the previous meeting having been read and confirmed, the chairman announced that the seventh volume of the “ Transactions of the New Zealand Institute” was now published and would be issued to the members, the only condition being that there were no arrears of subscriptions against their names. The following gentlemen were admitted members of the society :—Messrs. L. H. B. Wilson, H. C. W. Wrigg, It. P. Orme, C.E. The Chairman then called upon J. Carruthers, Esq., C. 8., to read his paper on “ Volcanic Action regarded as due to the Retardation of the Earth’s Rotation,” of which paper the following is a precis The cause of volcanic action is briefly as follows :—The retardation of the earth’s rotatatiou caused by the tides tends to elongate the earth’s polar axis. This tendency is resisted by the rigidity of the earth for some time, but eventually the strain becomes greater than the crust can bear, when the earth takes the form of equilibrium. The crust being rigid cannot fit the new shape of the inner part without fracture and crushing, which accordingly take place, each line of fracture becoming a line of elevation. The resistance offered to compression is sufficient at the surface to raise the temperature of a mile of stone forty degrees for every foot of compression ; at a depth of 200 miles, which is taken in the paper, It the sake of illustration, as half the thickness of the rigid crust, the same amount of compression would raise the temperature of a mile of stone by not less than 20,000 degrees, on account of the increased resistance caused by the greater elasticity of the inner parts of the earth. The sudden and great elevation of temperature which takes place at each line of fracture is transmitted at the rate of about a mile a second along the crust, and as soon as any part of it reaches the surface the stone forming the crust expands, the heat is then imprisoned, aud a range of mountains arises. It is calculated in the paper that the retardation which takes place in 150,000 years would in this manner cause the elevation of a range of hills 10,000 miles long, 1000 miles wide at the base, and 360 ft. high. Volcanoes, hot springs, and earthquakes are stated to be mere local and superficial effects of the primary elevatisn, and to be due to the inability of the rigid surface rocks to adapt themselves to the new shape of the underlying mass. They occur therefore more frequently on the flanks of the great lines of elevation than on the summit, and it is only where action is very violent, as in the Andes, that the deep-seated primary movement is intense enough to cause volcanic eruptions. Exception was taken to the theory that the temperature of the earth increases one degree for every 50ft. in depth, which was shown to be due to the same cause as ear-thquakes, and to bo not universally true. It was also stated that there was no reason whatever to believe that the inner parts of the earth are or ever have been fluid, or that the temperature is nearly so much greater than that of the surface as is generally stated to be the case. The paper concluded by comparing the results deduced from the theory with experience. It was the general opinion of the meeting that the discussion of this paper should be deferred until next meeting, which would give the members an opportunity for reading the paper, and forming opinions thereon. The paper by J. C. Crawford, Esq., F.G.S., on “The Igneous Rocks of Wellington” was read, in his absence, by the chairman. The paper pointed out in a lucid manner the course that past explorations had taken in regard to the igneous rooks of this province, and indicated the direction that future explorations should take.
The reading of this paper concluded the programme of the evening.
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New Zealand Times, Volume XXX, Issue 4500, 23 August 1875, Page 2
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697PHILOSOPHICAL SOCIETY. New Zealand Times, Volume XXX, Issue 4500, 23 August 1875, Page 2
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