Earth and Moon.

Progress, Volume I, Issue II, 1 September 1906, Page 297

Earth and Moon.

The following bears on a subject much discussed at the time of the San Francisco earthquake: — "In regard to the paroxysms of Vesuvius," says Professor Calmien, " they were most violent at the period of new and full moon;" and Professor Alexis Perrey, of Dijon, after tabulating catalogues of earthquakes, came to the conclusion that these were most frequent at new and full moon, and when our satellite was nearest to the earth. At the time of the Martinique eruptions they began when the moon's attraction was at a maximum over that part of the globe. The rigidity of the earth as a whole is great —greater than that of a globe of glass, probably equal to one of steel —but along lines of weakness, where volcanoes are situated, it may be less, and there differences of the moon's pull may be effective at critical times. The tide-producing effect of the sun and moon is enormously increased by nearness to the earth. On ioth April the moon was 223,100 miles distant ; on 29th March the distance was 252,100 miles. As a consequence, the attraction on the ioth ulto. was to that of the earlier date approximately at 16 to 11. Differences of atmospheric pressure must also tell at depths of the world's interior, especially if any considerable part of the mass is, as most persons suppose, still liquid. A fall in the barometer of iin. would

mean a reduction of pressure on every square mile of the earth's surface, sea and land alike, of about 870,000 tons, so that on the area covered by Vesuvius alone, over 100 square miles, the diminution of atmospheric pressure might easily amount to 10,000,000 tons. Influences there would not cause eruptions, but it is thought they might act as the last straw on the camel's back, in a condition of great strain.