Page:Popular Science Monthly Volume 89.djvu/45

 Popular Science Monthb/

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��"Ironing Out" Earthquake Wrinkles in San Francisco

AT the liim- of the earth- (jiiake many pavements of San Francisco "wrinkled" under the strain. Traffic since has increased the iine\en surface. By the use of the machine shown in the picture, old pavements are made like new. A traction -engine is fitted with an oil-blast furnace and a hood by which a section of pavement from the curb to the car track is softened until it can be leveled by raking. Each section is then success! \elysniui )t lied and rolled in the regulation way.

The most disastrous efifects of the earthciuake occurred in parts of the city where the ground consisted of "made" land, especially in a large area adjoining the Bay, which consisted originally of mud flats and overflowed lands built up with layers of sand, waste, and the like. Under the shaking of the eartii<iuake, this soft ground tended to flow along the slopes, causing pavements and street- car tracks to break up or buckle. Here and there the ground was rolled into waves three or four feet high. Where the texture of the soil was very loose, the ground surface was lowered. What occurred in the latter case was just what happens when a measure into which

���Intense heat from an oil-blast furnace is applied to breaks in the pavement so that it can be leveled

��gr.iin or loose sand has been pcjurcd is shaken in order to make it settle down. The shaking causes the particles to come closer together and the mass occupies less space. The rainfall had been much above the normal for three months before the earthquake, and the soil was there- fore more soft and plastic than usual.

Many observers in the region visited by this memorable earthquake have furnished graphic descriptions of the visible undulations of the ground that formed a feature of it, especially in soft alluvial soils. The waves were from one to three feet in height, and their length, according to one description, was about sixty feet from crest to crest. Trees and telegraph-poles were seen to rise and fall as the billows of earth swept by.

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��How Automobiles Innocently Break Windows HEN a heavy autouKjbilc runs over pebble may be caught just right by the pebbles no larger than a pea, a edge of the wheel and shot with such a

high velocity that a broken window is the result. One firm in New York has had three windows broken, all in the same frame. The lay- out at this particular place is as indicated in the drawing. The principle in\olved is the same as that prac- ticed in "shooting cherry stones" by pinching the slippery stones lietween the lingers. In this case, though, nuich higher velocities are attained because oi the enor- The heavy wheel of a motortruck shoots pebbles that mous loads nOW being placed

break unprotected windows On trucks.

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