The difference in price at the two periods is accounted for by the fact that their skins were much better in the latter, and the rabbits kept longer when killed; they must also have been larger. A skin before Michaelmas was only worth 1d., but soon after nearly 6d.; and in Hertfordshire was a warren where rabbit skins with silvery hair fetched 1s. each.[409] We have now reached the period when the result of Jethro Tull's labours was given to the world, his _Horse-hoeing Husbandry_ appearing in 1733. It is no exaggeration to say that agriculture owes more to Tull than to any other man; the principles formulated in his famous book revolutionized British agriculture, though we shall see that it took a long time to do it. He has indeed been described as 'the greatest individual improver agriculture ever knew'. He first realized that deep and perfect pulverization is the great secret of vegetable nutrition, and was thus led on to perfect the system of drilling seed wide enough apart to admit of tillage in the intervals, and abandoning the wide ridges in vogue, laid the land into narrow ridges 5 feet or 6 feet wide. He was born at Basildon in Berkshire, heir to a good estate, and was called to the bar in 1699, but on his marriage in the same year settled on the paternal farm of Howberry in Oxfordshire. In his preface to his book he throws a flash of light on country life at a time when the roads were nearly as bad as in the Middle Ages, so that they effectually isolated different parts of England, when he speaks of 'a long confinement within the limits of a lonely farm, in a country where I am a stranger, having debarred me from all conversation'.[410]