As Sir John Herschel has explained, science sometimes shows us that #things which we wish to do are really impossible#, as, for instance, to invent a perpetual motion, that is, a machine which moves itself. At other times science teaches us that the #way in which we are trying to make something is altogether the wrong way#. Thus, iron-masters used to think that the best way of smelting iron in the blast-furnace was to blow the furnace with cold air; science, however, showed that, instead of being cold, the air sent into the furnace should be made as hot as possible. Then, again, science often enables us #to do our work with a great saving of labour#. The boatman or bargeman takes care to learn the state of the tide, so that he may have the tide in his favour in making any journey. Meteorologists have now prepared maps of the oceans showing the sea-captain where he will find winds and currents most favourable to a rapid voyage. Lastly, #science sometimes leads us to discover wonderful things which we should not have otherwise thought it possible to do#; it is sufficient to mention the discovery of photography and the invention of the telegraph and the telephone. No doubt it may be said that all the greatest improvements in industry--most of what tends to raise man above the condition of the brute animals--proceed from science. The poet Virgil was right when he said, "#Happy is he who knows the causes of things.#" CHAPTER IV. DIVISION OF LABOUR. #25. How Division of Labour Arises.# When a number of workmen are engaged on any work, we find that each man usually takes one part of the work, and leaves other parts of the work to his mates. People by degrees arrange themselves into different trades, so that the whole work done in any place is divided into many employments or crafts. This division of labour is found in all civilised countries, and more or less in all states of society, which are not merely barbarous. In every village there is the butcher and the baker, and the blacksmith and the carpenter. Even in a single family there is division of labour: the husband ploughs, or cuts timber; the wife cooks, manages the house, and spins or weaves; the sons hunt or tend sheep; the daughters employ themselves as milkmaids. There is a popular couplet which says-- "When Adam delved and Eve span, Who was then the gentleman?" It seems to express the fact that this division of labour existed in very early times, before there were any gentlemen.