The Press., 1913-03-05
HEAT OF THE SUN
Old Sol Has a Strong Pull at the
 Capitol In Washington.
SWANS THE MAMMOTH DOME.

On . Hot Day His Torrid Rays Will Drag the Massive Iron Structure Way Out of Plumb-Turns the Same Trick With Washington Monument. Not many people have any idea as to the enormous amount of heat that the sun sends off into space. The earth gets only a, very small portion of 1t. The head Of pin placed twenty feet away from an electric light gets in proportion to the light on the sur rounding walls of room about what the earth gets of the suns light and heat radiated into space Yet that DOT tiOn the earth does get is great enough to cause great structures to move.
 In fact, all stone or metal buildings are constantly changing their positions under the hot rays of the sun. The great dome of the capitol building at
 Washington is the largest surface of cast iron in the world, and the effect of the continuous heat of a hot summer day can best be appreciated. says Har per'S Weekly, when 1t is known that this mammoth mass really sways back and forth under the scOrching rays un til the top feather in the cap of the statue of Freedom describes an ellipse the diameter of which on hot day varies from four to eight inches.
 The giant pIinth base of the dome, resting on the roof of the old sand stone building, measures 136 feet on side. The greatest diameter of the round dome is l25 feet. while the whole iron structure is 21S feet high from the old capitOrs roof to the base of Freedom on the apex. The cast iron covering this surface is made in thin sheets. offering a good cOnduG tor for the heat, which swells even the bolts and beams of the inside before the sun has made its circuit
 The southern side of the dome sui fers most from the heat. being expos ed longer to the sun, which passes south of the zenith while on it's jour ney from the east to the west. If the metal were exposed to constant heating the result of the continuation of such expansion as that received on very hot days might prove disastrous, but as it is little if any permanent in jury is done. since the iron returns regularly to its normal position as the cool night comes on.
 But what seems more remarkab ble is the fact that marble Is also changed in volume so perceptibly by the sunlight that the mammoth shaft of the Wash ingtOn monument sways back and forth in the sun on a hot day. The outer surface being of hard marble the expansion Is much greater than it would be had granite instead of mar ble been used. On a hot summer day the sharp aluminium apex that crowns the obelisk points to d position at least four inches north of normal. but al ways returns to its proper position iD the cool of the night
 From the extreme top of the monn ment inside long pipe line runs per pendicularly to the bottom. leading to small closet behind the elevator This contains long pendulum. whose bob hangs in a vessel of mercury. which prevents it's oscillation. Two stationary transits with highly mag nifying lenses are focused directly uIpOu lIC SuSI'CAOcu WNSs dlu these each Quiver of the monument is detected. being magnified on a fine Rcale graduated to thOusandths of an inch.
 Every morning at 10 o'clock a state mcnt of this plummet line is taken and reported to the war department. and 1t was by this means that the ef feet which the sums rays have on the huge white shaft was discovered This plumb bob of course. was placed In the monument for the purpose of de tecting any settling 1t might undergo. and. although the great weight of it's mass has pressed the ground for many decades. it has settled only slight fraction of an inch in one corner
 This seems extraordinary when it is realized that it's weight of 8l.72O tons rests on q foundation only I26E. feet square and 3S feet deep from a height almost fifteen times that of the depth The whole rests on the sandy bank of the Potomac river. with the enormous pressure of five tons to the square foot, Not only does the suns heat sway the big obelisk. but at times. when stiff winter gale was blowing, 1t has been reported as much as two inches out of plumb