The depth and strike of this fissure was determined by the observation that the area of greatest disturbance was along a curved line lying radial to the _epicentrum_. Such a condition it was assumed indicated that the fissure of origin must be inclined towards this area of greatest disturbance. A line was then drawn from this area to the _centrum_. A second line at right angles to this one gave the dip of the fissure. Höfer, when working on the earthquake of Belluno, came to the conclusion that the disturbance originated from two faults meeting each other at an angle of 60°. In this determination he was chiefly influenced by the form of a certain homoseist which was of the form of an elongated ellipse met on one side by a second ellipse, the principal axes of the two ellipses giving the strike of the two faults. CHAPTER XII. DISTRIBUTION OF EARTHQUAKES IN SPACE AND TIME. General distribution of earthquakes—Occurrence along lines—Examples of distribution—Italian earthquake of 1873—In Tokio—Extension of earthquake boundaries—Seismic energy in relation to geological time; to historical time—Relative frequency of earthquakes—Synchronism of earthquakes—Secondary earthquakes. _General distribution of earthquakes._—The records of earthquakes collected by various seismologists lead us to the conclusion that at some time or other every country and every ocean in the world has experienced seismic disturbances. In some countries earthquakes are felt daily, and from what will be said in the chapter on earth pulsations it is not unlikely that every large earthquake might with proper instrumental appliances be recorded at any point on the land surfaces of our globe. The area over which any given earthquake extends is indeterminate. The area over which an earthquake is sensible is sometimes very great. The Lisbon shock of 1755 is estimated as having been sensible over an area of 3,300 miles long and 2,700 miles wide, but in the form of tremors and pulsations it may have shaken the whole globe. The regions in which earthquakes are frequent are indicated in the accompanying map, which, to a great extent, is a reproduction of a map drawn by Mallet. The regions coloured with the darkest tint are those where great earthquakes are the most frequent. The actual number of earthquakes which have been felt in the differently coloured areas are given, when speaking of the relation of seismic energy to season.