202 



DESCRIPTION OF A BORING TUBE* 



VIII. 



Defcriptton of 

 the American 

 bcnci. 



Popular erpla- 

 nation of its 

 a^ion. 



DefcriplioH of a Boring Tube, in general Ufe in America ; bat 

 lej's known in this Country, 



Jl IG. 2. Plate X. exhibits a very fimple and ingenious borer, 

 confifting of the common center bit of the carpenters followed 

 by a wide flat thread fcrew, hammered up from a plate of iroi> 

 or fteel. It is faid that they are ufed to bore holes feveral feet 

 in length, and the peculiar property polTefled by this inftru, 

 ment is, that it clears the cutting without requiring to b6 drawti 

 out, as is the cafe with the augur, the gimblet, and other Cmi- 

 lar tools. I do not, however, think that it would have this 

 efTedl in boring perpendicularly down to confiderable depths; 

 bdt for horizontal or llightly inclined holes, its etfe6l muil fully 

 anftver. 



It may not at firft occur to the reader why the introduflion 

 of this tool into a hole which muft contain the wood that for- 

 merly blocked it up, fliould not be attended with fome degree 

 of impediment or jamming; but this difficulty will vanifh, 

 when it is confidered that the cuttings are, partly by their 

 weight, and partly by fridion againft the internal cylindrical 

 furface, prevented from revolving along with the fcrew. 

 The confequence is that they are prefled againfi: its thread, 

 and Hide along it towards the handle. And as this motion or 

 fhifting of the thread is quicker than the motion of boring, by 

 which the whole tool is carried inwards, the cuttings mult 

 come out with a velocity nearly equal to the difference of thefe 

 two motions. 



IX. 



Geographical and Topographical Improvements. By John 

 Chcrchman, Ej'q. M. Imp. Acad, of Sciences, Peterf- 



hurgh 



I 



C t alu of -^'^ appears to be a matter of much importance to the people 

 topographical of any Country, at all times, whether in war or jSeace, topof- 

 knowledgc. 



* From tUe Tranf. of the Soc. of Arts for 1804, who voted the 

 filver medal to him for the fame. 



fefs 



