Description of a Plough-car. 7g 



ascribe tliem to some other origin than the earth we in- 

 habit; and none so likely as coming from our neighbouring 

 planet. 



" Upon the whole then it appears highly probablCj that 

 the flaming meteors, and the burning atones that tall on 

 the earth, are one and the same thing. It also appears im- 

 possible, or in the extremest de2;ree miprobable, to ascribe 

 these, cither to a formation in the superior parts of the 

 atmosphere, or to the irruptions of terrestrial volcanoes, or 

 to the generation by lightning striking the earth. But, on 

 the other hand, that it is possible for such masses to be 

 projected from the moon so as to reach the earth ; and that 

 all the phosn'jmena of these meteors or failing stones, having 

 a surprising conformitv with the circumstances of masses 

 that may be expelled from the moon by natural causes, unite 

 in forming a body of strong evidence, that this is in all pro- 

 bability and actually the case." 



XII. Di'scriplio.'i of a Plough-ear which offers the least 

 possible Resistance, and which viaij be easily constructed. 

 By Mr. Jkffhrson, President of the United States ()f 

 America * . 



JL HK body of a plough ought not only to be the continua- 

 tion of the wing of the sock, beginning at its posterior edge, 

 but it must also be in the saniu plane. Its first function is 

 to receive horizontally from the sock the earthy to laise it 

 to the height proper for being turned over j to present in 

 its passage the Last possible resistance, and consequently to 

 require only the minivmvi of moving power. Were its 

 functions confined to this, the wedge would present, no 

 doubt, the properest form for practicef ; but the object is 

 also to turn over the sod of earth. One of the edges of the 

 tar ought then to have no elevation to avoid an useless 

 wasting of force; the otiicr edge ought on the contrary to 



• From Ann'tlcs (111. Musiiiw, Naiional d'Hislohe Ni tiirclle, no. 4. 1803. 



f I am sensilile that if die Gbject were merely to r m-c tl;e sod of earth to 

 a giver. Iieight by a dett-rminate lenjjth of ear, wit'iout turning it over, the 

 iJrm vvhicli WLuld g'.ve tlii least redjtance would not he c^'actly that of 3 

 wedge '.vith tuu plane f.itcs ; but the upper face ought to be curvilinear, 

 accordinj^ to ihc laws of the solid of leas: resistance described by mathexna- 

 ticians. Hat in thi j ca'C the dlfl'trcnce between the ell'ect of the v.edjje with 

 a curved face, and tiiat of a wedge with a plan? face, is so sir.al!, and it 

 '.'.oi'M hi: M difiiciilt lor workmen to construct the former, that '.he wedg« 

 v/iih a plane fare oujflit lo be preferred in practice aj the first citrui-nt cf 

 t/ur inethod of constraciiou. (iVu.*e 'if'tln' A', .'no:;.) 



J go 



