. St. Nicholas [serial]. s before, two inspec-tors had carefully examined the elevator andreported it in good condition. After the disaster, careful search was made for the cause of theaccident. When the broken wire cable was in-spected it was found that some of the strands weredefective; but as they were on the inside of thecable, it had been impossible to detect them whenthe previous examination was made. It is not friction alone that wears out a steelcable—or any piece of steel, for that a piece of soft wire, bend it sharply, andthen straighten it out again. Apparently it willbe
. St. Nicholas [serial]. s before, two inspec-tors had carefully examined the elevator andreported it in good condition. After the disaster, careful search was made for the cause of theaccident. When the broken wire cable was in-spected it was found that some of the strands weredefective; but as they were on the inside of thecable, it had been impossible to detect them whenthe previous examination was made. It is not friction alone that wears out a steelcable—or any piece of steel, for that a piece of soft wire, bend it sharply, andthen straighten it out again. Apparently it willbe as strong as ever. But keep on bending itback and forth at the same point, and sooner orlater it will break. This treatment crystallizesthe metal and makes it brittle. As a cable runsover a pulley, it is bent and straightened outagain. To be sure, the bend is not a sharp one;but the continued bending and straightening intime makes itself felt, and the strands of the cablebegin to give way, one after the other. As each. KEEPING A RECORD OF THE LIFE1135 OF AN ELEVATOR CABLE 1136 NATURE AND SCIENCE FOR YOUNG FOLK |0CT. strand breaks, the rest of the strands have tosustain a heavier load, until the weakened cablesuddenly snaps under the weight it has to carry. Of course, cables are carefully tested beforebeing installed, and it is generally known how longa cable may be used with safety before it shouldbe replaced with a new one. To be on the safeside, the cables are usually discarded before theyhave lived their whole useful life; but now andthen, as in the elevator accident referred to, thereis some hidden defect in the cable that brings it toan unexpected and untimely end. How can we foretell such an event? A wiremay be severely strained without showing anysigns of distress until just before it gives can we look into the heart of the metal andsee what serious changes are taking place insideof it? X-rays wont help us, because they giveus merely a shadow picture of the me
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Keywords: ., bookauthordodgemar, bookcentury1800, bookdecade1870, bookyear1873
