TOOLS. 



CHAPTER IV. 



POLISHING TOOLS. MEASURING TOOLS. 



Files and Sand-papers. The Sheffield File and its Structure. The Equisetum, 

 Mare's Tail, or Dutch Rush. Beauty of its Surface when seen through the 

 Microscope. Sand-paper. Skin of Dog-fish, Skate, and Shark. Skate- skin 

 used for Sword-handles. Distinction between the File and Sand-paper. 

 Measuring Tools. The Plumb-rule and the Level. Their Use in Tunnelling. 

 The Measure and its Uses. The Two-foot Rule and the Tape Measure. 

 Ovipositor of Gall-fly. Tongues of the Woodpecker, Wryneck, and Creeper. 

 The Spirit-level and its Uses. Theodolite and Callipers in Nature and Art. 

 The Contouring-glass. Pincers of Earwig again. Jaws of Insects. 

 The great Sialis of Columbia. 



FILES AND SAND-PAPERS. 



HAVING now examined the analogies between the cutting, 

 boring, striking and grasping tools of Nature and Art, 

 we come to those finishing tools which smooth and polish the 

 surface. 



The first is the File, an instrument which needs but little 

 description. It consists of a surface of hardened steel, broken 

 up into rough-edged teeth of infinite variety, according to the 

 work which the file has to do. It is rather remarkable, by the 

 way, that at present the English files are infinitely superior to 

 those produced in any other part of the world ; that their teeth 

 are all made by hand ; and that a genuine Sheffield file will first 

 cut its way through a piece of iron in half the time that would 

 be occupied by a file of any other nation, and then would easily 

 cut its antagonist in two. 



As long as the File is intended to work upon metal, there is 

 little difficulty in its manufacture, except that no machinery 

 has yet been invented which can give the peculiar edging of 



