The author does not wish to be understood as meaning that migration to cities is wholly desirable; for he is familiar with its disadvantages and dangers. But whether it be desirable or not is beyond the scope of this book. This book is merely a modest attempt to point out the influence of invention in making the world what it is today. Perhaps it would have been better if men had had no invention and had remained in a state of savagery. Some men say so sometimes; but even those men (or most of them) like to sit by a warm fire in a cozy room when it is cold outdoors. The consensus of opinion seems to be that civilization in the main has been a blessing to men, though not an unmixed blessing, and though men must keep on their guard against certain manifest dangers which civilization entails. In the same year, 1834, Jacobi invented an electric motor and Runge made the important discovery of carbolic acid. In 1835 Burden invented a horse-shoe machine. In 1836 four important inventions added four important parts to our rapidly growing Machine. The first was the "constant battery" invented by Daniell. Before this time a Voltaic cell, or battery, soon lost its strength, because of various chemical actions inside the cell which need not be detailed here. Daniell overcame this difficulty almost wholly by inventing a battery, in which there were two liquids instead of one, and the two liquids were in two separate compartments but separated only by porous material. This invention was successful from the start, and immediately increased the usefulness of Voltaic batteries and the means of utilizing electric currents. The second great invention in 1836 was that of acetylene gas made by Edmund Davy. It is still the most brilliant illuminating gas we have, and is rivaled by the electric arc-light only. The third invention was that of the revolver, made by Samuel Colt. It may be objected by some that the revolver did not contribute anything valuable to the Machine of Civilization because it was merely an improvement on the pistol, and enabled one to kill more men in a given time than he could before. Such an objection would have much to justify it; but it may be pointed out that the Machine must be made self-protective as far as possible; and that anything which increases the power of civilized man as against the savage, or barbarous, or semi-barbarous increases its power of self-protection. It is true that a savage can use a revolver, if he be instructed; but the more complicated a weapon is the more difficult it is for a savage, as compared with a civilized man, to use it effectively. This is not an argument in favor of complication for its own sake; but it is an argument in favor of accepting complication in a weapon, if the complication renders greater effectiveness possible.