259 



of the earth, communicating to the latter its well known wave-like 

 oscillation. 



In the course of these demonstrations it was shown, that a com- 

 parison of the respective times of the arrival of an earthquake at 

 three sufficiently distant places triangularly situated within the in- 

 fluence of the undulation, will enable us to calculate approximately 

 the path and velocity of the wave, in all cases where it has, as in the 

 instance before us, the form of a nearly straight line. 



Major Graham had noticed the earthquake of the 8th of 

 February last, at his house in Washington, at the N. W. cor- 

 ner of F. and Twentieth street West, three squares west of the 

 Navy Department. The last and most severe shock which he 

 felt, occurred at ten minutes before ten in the morning, mean 

 solar time. 



He felt the first agitation at about fifteen or twenty minutes before 

 10 o'clock, A. M. He was aroused from imperfect sleep, by a tremu- 

 lous motion of the bed, which he at once referred to a slight shock 

 of an earthquake. Having fallen into a doze again, he was a second 

 time aroused by a similar shock, quite evident, though not severe: it 

 caused the furniture in the room to shake. Soon afterwards he felt 

 a third shock, so intense as to produce some apprehension that if it 

 increased any in force, the house might fall. There was a sensible 

 oscillation or rocking motion of the bed from north to south, or trans- 

 verse to the direction in which he lay at that time. The furniture in 

 the room shook with some violence, and a looking-glass, which stood 

 upon a bureau, suspended within a square frame, standing in the 

 usual manner upon a pedestal with drawers, was set to oscillating 

 through an angle of about 50°, or 25° from a perpendicular in each 

 direction. This last shock occurred at 9h 50m, A. M., as observed 

 by Major G. in his room. Its severity caused him to rise and join 

 the other members of his family. On entering the room of one of 

 them, who was an invalid, in the second story of the house, and imme- 

 diately below the room occupied by himself, and on inquiring if the 

 shock was noticed, the reply was, that two distinct and evident shocks 

 had been felt, the last and most severe, at 10 minutes before 10 

 o'clock, as noted by a mantel clock which was in view at the time. 

 The bed in which the invalid lay was caused to undulate sensibly, 

 from north to south, or longitudinally of its direction. At the same 

 time, a bunch of keys, attached to a metallic ring, hanging by a 



