ORIGIN OF THE PLOW AND WHEEL-CARRIAGE. 453 



been recently invented, and was used for land already under tillage. 

 He also mentions the coulter {cultei'). This knife, fixed in front to 

 make the first cut ready for the share to turn the sod, is a great im- 

 provement on the primitive plows, where the plowshare has to do the 

 whole work. In Pliny's time, though only forming part of some 

 plows, it was evidently well known. 



Thus he recognizes the whole con- ^"'- ^'^ 



struction of the wheel-plow (Fig. 

 10) as figured by Caylus from an 

 ancient gem. The ordinary mod- 

 ern plow used by the English 

 farmer improves upon this rather 

 in details of construction and ma- 

 terial than in essential principle, 

 though a new start in invention is 



taken by the self-acting plow, which no longer needs the plowman to 

 follow at the plow-tail, and by the steam-plow, which substitutes 

 engine-traction. 



The plow, drawn by oxen or horses, and provided with wheels, has 

 taken on itself the accessories of a wheel-carriage. But, when the plow 

 is traced back to its earliest form of a hoe dragged by men, its nature 

 has little in common with that of the vehicle. Though the origin of 

 the wheel-carriage is even more totally lost in prehistoric antiquity 

 than that of the plow, there seems nothing to object to the ordinary 

 theoretical explanation (see Reuleaux, "Kinematics of Machinery," 

 and others), that the first vehicle was a sledge dragged along the 

 ground ; that, when heavy masses had to be moved, rollers were put 

 under the sledge, and that these rollers passed into wheels, forming 

 part of the carriage itself. The steps of such a transition, with one 

 notable exception which will be noticed, are to be actually found. 

 The sledge was known in ancient Egypt (see the well-known painting 

 from El Bersheh of a colossal statue being dragged by men with ropes 

 on a sledge along a greased way, Wilkinson, "Ancient Egyptians," 

 vol. iii). On mountain-roads, as in Switzerland, as well as on the snow 

 in winter, the sledge remains an important practical vehicle. The use 

 of rollers under the sledge was also familiar to the ancients (see the 

 equally well-known Assyrian sculpture of the moving of the winged 

 bull, in Layard's " Nineveh and Babylon," p. 110). If, now, the middle 

 part of the trunk of a tree used as a roller were cut down to a mere 

 axle, the two ends remaining as solid drums, and stops were fixed 

 under the sledge to prevent the axle from running away, the result 

 would be the rudest imaginable cart. I am not aware that this can be 

 traced anywhere in actual existence, either in ancient or modern times ; 

 if found, it would be of much interest as vouching for this particular 

 stage of invention of the wheel-carriage. But the stage which would 

 be theoretically the next imjorovement is to be traced in practical use ; 



