4 2 



THE POPULAR SCIENCE MONTHLY. 



An illustration of the remarkable strength and elasticity of the 

 foundation lines of orb-webs appears in a biographical notice of the 

 distinguished astronomer, the late General Ormsby M. Mitchell, 



printed with an 

 edition of his lect- 

 ures. Prof. Mitch- 

 ell directed his 

 great ingenuity to 

 the problem of 

 causing a clock to 

 record its beats 

 telegraphically, 

 and at the same 

 time perfectly per- 

 form the work of 

 a time - keeper. 

 The required 

 makes and breaks 

 in the battery 

 were effected by 

 means of a cross 

 of delicate wire 

 and a mercury- 

 cup. Many obsta- 

 cles having been 

 overcome, there 

 arose the great 

 difficulty of pro- 

 curing a fiber suf- 

 ficiently minute 

 and elastic to con- 

 stitute the physical union between the top stem of the cross 

 and the clock pendulum. Various materials were tried, among 

 others a delicate human hair, the very finest that could be ob- 

 tained, but this was too coarse and stiff. Its want of pliancy 

 and elasticity gave to the minute " wire cross " an irregular mo- 

 tion, and caused it to rebound from the globule of mercury into 

 which it should have plunged. " After many fruitless attempts," 

 says Prof. Mitchell, " an appeal was made to an artisan of wonder- 

 ful dexterity — the assistance of the spider was invoked ; his web, 

 perfectly elastic and perfectly pliable, was furnished, and this 

 material connection between the wire cross and the clock pendu- 

 lum proved to be exactly the thing required. In proof of this 

 remark I need only state the fact that one single spider's web has 

 fulfilled the delicate duty of moving the wire cross, lifting it, and 

 again permitting it to dip into the mercury every second of time 



Fig. 1.— Sector of a Dew-laden Orb-web. (Magnified.) 



