The first really scientific description of an earthquake--that of Lisbon--with its far-reaching accompanying phenomena, was the work of the greatest contemporary thinker, Kant, and it is not too much to say that his paper opened a new epoch in the knowledge of earthquakes. That terrible event and the extreme terror which it caused everywhere were followed in 1783 by the likewise extremely destructive earthquake of Calabria. The attention of the people was thus directed to this mysterious mighty activity of the earth, and was kept especially lively in Italy, the country of Europe most subject to earthquakes. The newly rising science of geology therefore found in the last third of the last century in these phenomena a problem of prominent importance. Geologists were the first to apply themselves to seismic studies, as the most widely current explanation of the phenomena is still a geological one. The scientific interest of the question prevailed over the practical. More attentive observation was given to earthquakes, the accounts of them scattered through the ancient chronicles were collated, and the already very numerous seismic notes of great earthquake manifestations--such as those by Hoff, Perry, Mallet, Volger, Fuchs, etc.--constituted a very important factor in the study. One of the earliest results of the inquiry was to show that directly perceptible earthquakes are not perceptible everywhere; that they are most common on the great upfoldings of the earth's crust on the mountain chains, such as the Andes, Alps, and Himalayas; and that, further, they are connected with the shores of the Pacific, the Antilles, and the Mediterranean, and with places also where great breaches and various disturbances are evident; that they are at home likewise in volcanoes; and that they are most frequent in the northern hemisphere, and when the earth is nearest to the sun. The descriptions of powerful shocks furnish us evidence of a double movement of the earth's crust--an alternate up-and-down vibration and an often very marked wave motion. The destruction which earthquake shocks and waves inflict on buildings, and the remarkably rapid and wide spread of the tremblings over the surface of the earth, have been very diligently inquired into; and when, in 1856, Naples and Calabria were visited by a great earthquake, an English investigator, Robert Mallet, made a full study of it, and believed that by comparing the direction of the rents in walls and buildings, which were assumed to correspond with that of the tremblings, he could identify the focus of the shocks in the earth's interior, and the course of the wave movement over its surface--a view which has long prevailed in seismology. Still more important was the work of the geologist Karl von Seebach, of Göttingen, on the great earthquake in central Germany, which kept the northern part of the plains of the upper Rhine, around Mayence, Grossgerau, and Darmstadt, disturbed for several years after 1869. Von