306 SYSTEMS OF PERMANENT AGRICULTURE 



before they can be equally spread upon the land. No pieces should exceed 

 the size of marbles^ To perform this necessary operation, I would recommend 

 the bones to be sufficiently bruised by putting them under a circular stone, which, 



^ being moved round upon its edge by means of a horse, in the manner that tan- 

 ners grind their bark, will very expeditiously effect the purpose. At Sheffield 

 it is now become a trade to grind bones for the use of the farmer. Some people 

 break them small with hammers upon a piece of iron, but that method is in- 

 ferior to grinding. (-To ascertain the comparative merit of ground and unground 

 bones, I last year dressed two acres of turnips with large bones, in the same 

 field where the ground ones were used ; the result of this experiment was, that 

 the unground material did not perform the least service; while those parts of 

 the field on which the ground bones were laid were greatly benefited. 



"I find that bones of all kinds will answer the purpose of a rich dressing, but 

 those of fat cattle I apprehend are the best. The London bones, as I am in- 

 formed, undergo the action of boiling water, for which reason they must be 

 much inferior to such as retain their oily parts; and this is another of the many 

 proofs given in these essays that oil is the food of plants. The farmers in this 

 neighborhood are become so fond of this kind of manure, that the price is now 

 advanced to one shilling and fourpence per bushel, and even at that price they 

 send sixteen miles for it. 



"I have found it a judicious practice to mix ashes' with the bones; and this 

 winter I have six acres of meadow land dressed with that compost. A cart 

 load of ashes may be put to thirty or forty bushels of bones, and when they have 

 heated for twenty-four hours (which may be known by the smoking of the heap) 

 let the whole be turned. After laying ten days longer, this most excellent dress- 

 ing will be fit for use." Jj 



In 1822, William Corbett, in his compilation of the writings of 

 JethroTull, made the following statements: 



"Mr. Tull's main principle is this, that tillage will supply the place of 

 manure; and his own experience shows that a good crop of wheat, for any 

 number of years, may be grown every year upon the same land without any 

 manure from first to last." 



" Mr. Tull continued his wheat crops to the harvesting of the twelfth upon the 

 same land without manure; and when he concluded his work, he had, as he in- 

 forms us in a memorandum, the thirteenth crop coming on, likely to be very 

 good." 



It may be stated, however, that, after the time of Jethro Tull 

 and before Corbett's republication of the Tullian methods and 

 theories, some truly scientific facts had been discovered. In fact, 

 chemistry had begun to assume the character of an exact science. 

 Priestly had discovered oxygen and also identified as oxygen the 

 gas which others had previously observed is given off from the 



