138 PROCEEDINGS OP THE [July, 1887. 



I of an inch to an inch on that floor, with a regularity that was striking. While, 

 on the other hand, such buildings as the three churches of St. Michael's, St. 

 PhiUps and the Scotch Presbyterian, aU three of which have more length than 

 height, and the said length being in a direction East and West, could not under 

 the circumstances sway back and forth from the nature of their proportions. 



Their steeples or towers could rock, as they unquestionably must have done, 

 but the effect of the waves- upon the buildings themselves, which has been so 

 difficult to explain, can probably be accounted for by their having encountered, 

 as they passed under the walls, an imjdelding mass of heavy masonry, not sus- 

 ceptible of any oscillating movement, which was consequently rooted up by 

 their irresistible progress, and made to crack in many directions, as also, in 

 some instances, to lean from the perpendicular. 



The leaning out of the four walls of the main central part of the Charleston 

 College builduig was a marked feature of the damage done. The masonry there 

 is of the most substantial kind, antedating the introduction of stone lime, and 

 for the injury that was done to have occurred to such a perfect specimen of sub- 

 stantial brick work, proves how irresistible the waves were at that point. T^ey 

 were unable to detach the bricks from the mortar, as there was scarcely a crack 

 to be seen afterwards, but they had the height and the violence necessary to 

 make every outer wall lose its perpendicular position. There was nothing to 

 indicate in the College building the direction from which the shocks came, and 

 no clue as to direction could be obtained by the displacement of the horizontal 

 cases on the floor of the Museum. 



With regard to the oscillating or rocking movements, Dr. Manigault stated 

 that he had tested the matter in company with an intelligent friend, and the 

 conclusion seemed irresistible that, as the first wave reaches a building, it raises 

 the end first reached, and causes the structure to tilt in the opposite direction. 

 This can be illustrated by holding a volume upon a table, in the vertical posi- 

 tion which it maintains on the shelves of a book-case, and sUghtly tilting it in 

 one direction, as a round ruler, representing an earthwave, is inserted under the 

 raised edge. As there is an appreciable distance between the crests of the waves, 

 the structure has time to retimi to its normal position, and even somewhat be- 

 yond it, before the second wave strikes it, and thus the rocking motion is pro- 

 duced. 



This seems simple enough and scarcely requiring explanation, but it is dwelt 

 upon in consequence of the beUef being very general that the effect of the first 

 wave is to cause the structure to lean in the direction from which the wave 

 has come, instead of the reverse, as has been explained. To produce a tilt in 

 the direction from which the wave has come, it would be necessary for the en- 

 tire base of a structure or column to be moved some distance in its bed. If 

 this should occur the displacement of houses would be endless, and confusion 

 would reign among neighboring proprietors, in consequence of changes in 

 boundary lines ; whereas no such complications have been the result of the re- 

 cent earthquake. 



i 



