Benton — Strength and Elasticity of Spider Thread. 75 



Art. VIII. — The Strength and Elasticity of Spider Thread; 

 by J. R. Benton, Ph.D. 



The writer of this note happened to notice a spider thread 

 of such extraordinary thickness and length (0'01 cm in diameter ; 

 2"5 m long) as to suggest the idea of measuring its physical 

 properties, since this could easily be done with the thread in 

 question, though it would be exceedingly difficult with spider 

 threads of the usual size. 



The results may be of interest for the following reasons : 



(1) as furnishing a test of the popular idea that spicier threads 

 are composed of a substance of extraordinarily great strength ; 



(2) on account of the occasional technical application of spider 

 threads in the reticules of scientific instruments ; and (3) 

 because the material of the thread, in its chemical nature, is 

 placed among the proteids, which usually have peculiar 

 mechanical properties. On account of the great complexity 

 of chemical structure of the proteids, their physical properties 

 may be especially useful in determining their relationships 

 with one another. In the present instance, the mechanical 

 properties of spider thread may furnish ground for deciding 

 whether or not its material is identical with silk, as is some- 

 times asserted. 



A spider thread, as is well known, is not usually composed 

 of a single fiber, but of a number of fibers adhering together 

 more or less closely. In the thread used for the present study, 

 the number of component fibers was very large. It was not 

 feasible to count them directly ; but single fibers, when sepa- 

 rated from the main thread, could be seen to have a diameter 

 less than one-twentieth of that of the main thread. This 

 would indicate several hundred fibers in the main thread, if it 

 can be assumed that all of the component fibers have the same 

 size. The component fibers appeared to adhere together only 

 very loosely ; at some places bundles of them were distinctly 

 separate from the rest of the thread. Under such circum- 

 stances the apparent cross-section of the thread varied greatly 

 from point to point. The true cross-section must be known in 

 order to determine the mechanical properties of the material ; 

 and as it was not feasible under these circumstances to ascer- 

 tain the true cross-section, the thread was twisted, so as to 

 bring all of the component fibers into one compact mass. 

 The twist applied amounted to three revolutions for each cen- 

 timeter of length, and it resulted in bringing the fibers together 

 into a cross-section of fairly perfect circularity. The diame- 

 ter, as measured by a micrometer microscope, varied from 

 point to point between the limits '0076 cm and -0103 cm . 



