Democratic Sentinel, Volume 19, Number 31, Rensselaer, Jasper County, 9 August 1895 — TALL TOWERS SWAY TO AND FRO. [ARTICLE+ILLUSTRATION]

TALL TOWERS SWAY TO AND FRO.

A'.Rigid Structure Would Inevitably Collapse. Every person who has looked upward on a tall smokestack or monument or shot tower has been impressed with the idea that the object had an oscillation.

( People who know all \about the subject ex- ' plained it to themselves or to others, but “there are others,” who did not know whether movement was actually in the object or in their own eyes. Well, such objects do move. Take the tall chimney of the West Chicago street railway power house, of which there is a cut in this explanation. It has an oscillation equal to about two feet, which is indicated by the dotted lines. The oscillation begins at the center of gravity of the tower. Some of these towers

sway more than others, but they all sway. A man to whom a reporter put the question said, substantially: “If such an object did not have that vibratory movement it would fall. There is no such thing known in mathematics as rigidity. The earth is in constant motion. I have tested' that and proved it, and so have others.”” “What causes this oscillation in a tower or monument or smokestack?" “Three things—the condition of the earth upon which it stands, the effect of the heat and cold and that effect depends upon the material out of which the object is constructed, and, third, the wind. And then, again, the manner in which the object is constructed has something to do with the movement of which you speak. The expansion by heat is about 1 in 800 for wrought iron, nearly the same for steel, 1 in 800 for

brick, and three times as much for sandstone. This is for a warming up of 180 degrees. “The oscillation due to wind Is easily understood except that everybody Is not aware the wind acts in gusts even when to the ordinary observer it may seem to be steady. The pressure of wind for every square foot of surface that is exposed to It (perpendicularly) varies from little more than nothing up to some 50 pounds for the highest possible wind velocity In this part of the world. “The third kind, due to ground tremblings, is the least except at times of earthquake shock, but is none the less a fact Observations with large transit telescopes tend to sustain the theory that any particular section of the earth’s surface continually is changing in position of level, the same In principle, though vastly less In extent, than the change In level of the surface of a board that is floating bn a sheet of water the surface of which Is rufiled by the wind.”

A CHIMNEY'S VIBRATION.