Hence the importance for our ancestors that the separation _should_ be effected. Hence it arose in the middle ages, as a considerable object for chemistry, to discharge the writing from the roll, and thus to make it available for a new succession of thoughts. The soil, if cleansed from what once had been hot-house plants, but now were held to be weeds, would be ready to receive a fresh and more appropriate crop. In that object the monkish chemists succeeded; but after fashion which seems almost incredible; incredible not as regards the extent of their success, but as regards the delicacy of restraints under which it moved; so equally adjusted was their success to the immediate interests of that period, and to the reversionary interests of our own. They did the thing; but not so radically as to prevent us, their posterity, from _un_doing it. They expelled the writing sufficiently to leave a field for the new manuscript, and yet not sufficiently to make the traces of the elder manuscript irrecoverable for us. Could magic, could Hermes Trismegistus, have done more? What would you think, fair reader, of a problem such as this--to write a book which should be sense for your own generation, nonsense for the next, should revive into sense for the next after that, but again became nonsense for the fourth; and so on by alternate successions, sinking into night or blazing into day, like the Sicilian river Arethusa, and the English river Mole--or like the undulating motions of a flattened stone which children cause to skim the breast of a river, now diving below the water, now grazing its surface, sinking heavily into darkness, rising buoyantly into light, through a long vista of alternations? Such a problem, you say, is impossible. But really it is a problem not harder apparently than--to bid a generation kill, but so that a subsequent generation may call back into life; bury, but so that posterity may command to rise again. Yet _that_ was what the rude chemistry of past ages effected when coming into combination with the reaction from the more refined chemistry of our own. Had _they_ been better chemists, had _we_ been worse--the mixed result, viz. that, dying for _them_, the flower should revive for _us_, could not have been effected: They did the thing proposed to them: they did it effectually; for they founded upon it all that was wanted: and yet ineffectually, since we unravelled their work; effacing all above which they had superscribed; restoring all below which they had effaced.