494 



On the Elasticity of Spider Lines. 



the elastic limit is exceeded, the extension increases in a 

 greater proportion than the tension, in spider's thread, on the 

 contrary, the extension at first increases more slowly than the 

 tension, and afterwards goes on at exactly the same rate up to 

 the breaking-point. It will be seen that the latter part of 

 the curve is practically a straight line. 



Stress-Strain Diagram of Spider's Thread. 



The behaviour of spiders'' thread under stress is very similar 

 to that of muscle and all animal tissue. They show a kind of 

 tetanus tendency when stretched. It also resembles india- 

 rubber, as shown in a stress-strain diagram obtained by 

 Professor Archibald Barr in a testing-machine designed 

 by him. 



Subject to the error caused by want of circularity of the 

 thread, the Young's modulus was found to be 7*769 x 10* 

 grammes per square centimetre. This is much lower than 

 the value for any metal, the lowest being that of lead, which 



