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THE POPULAR SCIENCE MONTHLY. 



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tain number of times, until I have put sufficient torsion on the fibre D 

 to lift up the beam. Now, according to the law of torsion, the force 

 with which a perfectly elastic body like glass tends to untwist itself 

 is directly proportional to the number of degrees through which it 

 has been twisted ; therefore, knowing how many degrees of torsion I 



