Look again, as a result of the disturbing force of genius, at the effects of great inventions--how unexpected, complex, subtle, all but miraculous--throwing out alike the path of human history, and the calculations of the student. If physical discoveries produced only physical or economic results--if the invention of printing had only produced more books, and more knowledge--if the invention of gunpowder had only caused more or less men to be killed--if the invention of the spinning-jenny had only produced more cotton-stuffs, more employment, and therefore more human beings,--then their effects would have been, however complex, more or less subjects of exact computation. But so strangely interwoven is the physical and spiritual history of man, that material inventions produce continually the most unexpected spiritual results. Printing becomes a religious agent, causes not merely more books, but a Protestant Reformation; then again, through the Jesuit literature, helps to a Romanist counter-reformation; and by the clashing of the two, is one of the great causes of the Thirty Years' War, one of the most disastrous checks which European progress ever suffered. Gunpowder, again, not content with killing men, becomes unexpectedly a political agent; 'the villanous saltpetre,' as Ariosto and Shakespeare's fop complain, 'does to death many a goodly gentleman,' and enables the masses to cope, for the first time, with knights in armour; thus forming a most important agent in the rise of the middle classes; while the spinning-jenny, not content with furnishing facts for the political economist, and employment for millions, helps to extend slavery in the United States, and gives rise to moral and political questions, which may have, ere they be solved, the most painful consequences to one of the greatest nations on earth. So far removed is the sequence of human history from any thing which we can call irresistible or inevitable. Did one dare to deal in epithets, crooked, wayward, mysterious, incalculable, would be those which would rather suggest themselves to a man looking steadily not at a few facts here and there, and not again at some hasty bird's-eye sketch, which he chooses to call a whole, but at the actual whole, fact by fact, step by step, and alas! failure by failure, and crime by crime.