1886.] NKAV TOEK ACADEMY OF SCIENCES. 25 



"wagon ten times magnified. At the same time the building be- 

 gan to vibrate, the windows rattled and some light objects were 

 disturbed and fell to the floor. I was sensible of a tremor that 

 not only jarred, but swayed my body and caused my book to vi- 

 brate and swing in my hand. I recognized the nature of the 

 phenomena at once, observed the time and made a note of it. 

 Subsequently, going into the geological cabinet, I found palpable 

 evidence of the force of the vibrations. In a case occupied by 

 specimens of marble, many of which were set on edge against the 

 back of the case, all sucii were thrown down and some were 

 broken. As the back of the case was toward the north, this 

 proved that some of the vibrations were from that direction. 

 This earthquake was noticed by a number of observers, and 

 their testimony showed that the area affected was, as usual, el- 

 liptical in outline, and extended from Washington, D. C, to 

 Portsmouth, Me., and from Harrisburg, Pa., to the Atlantic. 



In the Old World, observations on earthquake vibrations have 

 been reduced to a system, and instruments called seismographs 

 or seismometers have been devised, which make an automatic 

 record of the time, direction, and force of the vibrations. 

 Where such instruments are scattered over a country it is evi- 

 dent that the outline of the area affected by an earthquake shock, 

 as well as the geographical position and depth of the centre of 

 motion, may be accurately determined. 



In Japan, where earthquake vibrations are almost incessant, 

 an extended system of observations has been instituted by Prof. 

 Milne, which are likely to throw much light upon this subject. 



In this country there are few seismometers, and no carefully 

 regulated system of observation has been yet adopted, but it is 

 probable that one good effect of the Charleston earthquake 

 will be to excite an interest in such phenomena that shall result 

 in the organization of a thorough system of observation. The 

 -officers of the Geological Survey and Signal Service Bureau are 

 taking an active interest in the matter, and it is probable that 

 observations on the movements of the earth will be added to 

 those they are now making on the movements of the atmosphere. 



When the data already collected in regard to the Charleston 

 earthquake shall have been tabulated, it will doubtless be found 

 that the displacements which occasioned the vibrations were lo- 

 cated along a line parallel with the Alleghanies and at a depth 

 of 10,000 to 20,000 feet, not under, but westward of the city. 



Inasmuch as no great change took place on the surface of the 

 land in South Carolina, it has been suggested that the seat of 

 the movement was under the ocean, and that important changes 

 may have taken place in the topography of the sea bottom. It 

 is quite certain, however, that such was not the case; for any 



