world-shaking effects there are about 30,000 small earthquakes every year, England's annual contribution to this number being about half a dozen. What is the meaning of a "great earthquake," and how do we define "small" earthquakes? A small earthquake is one such as we have described as taking place in the valley of the Mississippi, and which, even though it may produce considerable disturbance in its neighbourhood, is not perceptible at any great distance away. A great earthquake is one which sends its vibrations thousands of miles. A very large earthquake, originating in any part of the world, _may be recorded in any other part of the globe_. Although only a few people in Great Britain have been privileged to feel a home-made earth tremor, every one of us is very many times a year moved by earthquakes. We do not perceive them because the back-and-forth motion of the ground is performed too slowly, while if there is a movement of the ground the undulations are so very flat that they cannot be perceived. But at several places in England and at earthquake observatories (seismological stations) all over the world, from Japan to Australia and from South Africa to Greenland, instruments are set up which are sensitive enough to record these tremors, though not always to locate them. Sometimes when Professor Behar in Germany, or Mr. Milne from his observatory in the Isle of Wight, telegraphs to the newspapers that signs of a great earthquake have appeared on their instruments, the world hears no more of these disturbances. They have occurred we are certain, but the place where the great cataclysm which has thus shaken the whole round world took place has been fortunately remote from inhabited portions of the earth, and has very likely been beneath the waters of some ocean.