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On Artificial Cobwebs for Micrometers. 

 By C. R. Goring, M.D. 



A COMMON cobweb has always appeared to me to be a very 

 strong substance in proportion to its extreme tenuity, for a 

 bulky spider will frequently depend from a single fibre of great 

 length : — small insects are incapable of overcoming the resist- 

 ance of the meshes of a web ; — which will also endure for a 

 considerable time in wet and windy weather without requiring 

 much repair. Nevertheless, I have always found astronomers 

 extremely nervous about the threads of their micrometers, which, 

 it is said, may be destroyed by the trifling current of air which 

 passes through the tube of a telescope when its objective and 

 eye-glasses are displaced ; probably because the cobwebs, being 

 of animal origin, are subject to decomposition in course of time, 

 for I do not think a cobweb, fresh from the body of a spider, 

 could be so easily affected. Be this as it may, I have acciden- 

 tally discovered a mode of making artificial ones, which are not 

 subject to decomposition, which may be stretched by mechani- 

 cal violence to double their length without snapping, returning 

 again to their original dimensions — which maybe blown upon by 

 a powerful pair of bellows, with its nose close to them, without 

 injury, and which can be rendered of any degree of tenuity and 

 fineness, being a perfect substitute for the ordinary ones, as it 

 seems to me ; but as I am not a connoisseur in such matters, it 

 must be left to Messrs. Troughton and Sims, who have certainly 

 arrived at the extreme verge of improvement in the construction 

 of micrometers, to determine the point at issue between me and 

 the spider. The following is the receipt for making them : — 

 Procure some of the purest essential oil of turpentine, shave 

 some caoutchouc extremely thin, and put it into a small wide- 

 mouthed phial, observing not to fill it more than one quarter ; 

 pour in the turpentine to the top, and secure it carefully with a 

 cork and bladder. Let this be worn in the pocket for a few 

 days, and the India rubber will absorb the essential oil, and 

 become greatly increased in bulk ; then let a portion of it be 

 put into another bottle with some more turpentine, and in a few 

 days it will be completely dissolved. It is necessary that there 

 should be more turpentine employed in the first instance than 



JAN.— MARCH, 1827. G 



