78 Benton — Strength and Elasticity of Spider Thread. 



metals (modulus about 10 12 ), but does not at all approach such 

 a substance as rubber (modulus about 10" dynes per cm 2 ). 



Elongation at rupture amounted to about 20 per cent of 

 the original length of the thread. 



The thread showed a distinct elasticity of torsion ; but in 

 view of its complex structure, data on torsion can not have 

 any very definite significance, and accordingly are not pre- 

 sented. 



Specific Gravity. — A 10 om length of the thread, of mean 

 cross-section 5X10 -5 cm 2 , weighed 0"33 mg , which gives for the 

 specific gravity, 0*66. 



Comparison with Silk Fibers. — The mechanical properties 

 of silk fibers have been studied by Beaulard,* who found 

 for the tensile strength 2*85 XlO 8 dynes per cm 2 , and for 

 Young's modulus 6 - 50xl0 10 dynes per cm 2 . As these values 

 differ from those for the spider thread by amounts greater than 

 would be accounted for by experimental errors, it seems prob- 

 able that the material of the spider thread is different from 

 silk. 



University of the State of Florida, Gainesville. 



*F. Beaulard : Comptes rendus, cxxxv, pp. 623-626, 1902; Journal de 

 physique, ii, 785-795, 1903 ; quoted in Science Abstracts, 1903, p. 129, and 

 1904, p. 137. 



