+----------------------------+---------+--------+--------+ | | Moment |Distance|Velocity| | Localities |observed | from |in feet | | |of shock |presumed| per | | | | origin | second | +----------------------------+---------+--------+--------+ | | h. m. | ° ′ | | | Presumed focus, lat. 43°, | } 11 51 | -- | -- | | long. 11° W. | } | | | | Ship at sea in lat. 43°, | } | | | | many leagues from coast | } 11 52 | 0 30 | 3,091 | | of Portugal | } | | | | Ship in lat. 44° 8′ and | } 11 54 | 1 45 | 3,607 | | about 80 leagues from | } | | | | coast | } | | | | Corunna | 11 51 | 2 30 | 2,576 | | Ship lat. 44° 8′ and 80 | } | | | | leagues NNW. of Cape | } 11 58 | 3 30 | 3,091 | | Finisterre | } | | | | Lisbon | noon | 4 30 | 3,091 | | Madeira | 12 6 | 10 0 | 4,122 | | Cork | 12 11 | 9 30 | 2,937 | +----------------------------+---------+--------+--------+ These tables, owing to the nature of the materials which Mallet had at his disposal, are but rude approximations to the truth. Two interesting facts are, however, observable: the first being that the velocities for the earthquake of 1761 are much higher than those obtained for the earthquake of 1755; and, secondly, that in both cases the velocities as determined from the observations of ships at sea closely approximate to each other, in all cases being nearly the same as that with which a sound wave would travel through water. The great differences in transit velocity obtained for different earthquakes is a point worthy of attention. Seebach’s velocity is a _true_ transit velocity, and its determination is dependent on the assumption that the shock radiated from the _centrum_ and not from the _epicentrum_, Seebach’s method is explained when speaking about the determination of origins. Some interesting observations on the velocity with which the earthquake of October 7, 1874, was propagated, are given by M. S. di Rossi.[18] One assumption is that the disturbance radiated from an origin to surrounding points of observation, whilst another is that the disturbance followed natural fractures, the direction of which is derived from the crest of certain mountain ranges. These velocities are as follows, Maradi being at or near the origin of the disturbance:—