"Some ask," says La Bruyere, "why mankind in general don't compose but one nation, and are not contented to speak one language, to live under the same laws, to agree amongst themselves in the same customs and worship: for my part, seeing the contrariety of their inclinations, tastes, and sentiments, I wonder to see seven or eight persons live under the same roof, within the same walls, and make a single family." Molecular philosophy shows interspaces betwixt atom and atom, differing atoms, which can hardly be said to touch; so bodies are formed, and so society and public opinion are compounded. "The single individual is to collective humanity," says Alger, "as the little column of mercury in the barometer is to the whole atmosphere. They balance each other, although infinitely incommensurate. A quicksilver sea, two and a half feet deep, covering the globe, would weigh five thousand million tons. That is the heft of the air,--that transparent robe of blue gauze which outsags the Andes and the Alps. Its pressure is unfelt, yet if that pressure were annulled all the water on the earth would immediately fly into vapor. Public opinion is the atmosphere of society, without which the forces of the individual would collapse and all the institutions of society fly into atoms." Common sense has been defined to be the "average intellect and conscience of the civilized world,--that portion of intelligence, morality, and Christianity, which has been practically embodied in life and active power. It destroys pretense and quackery, and tests genius and heroism. It changes with the progress of society; persecutes in one age what it adopts in the next; its martyrs of the sixteenth century are its precedents and exponents of the nineteenth; and a good part of the common sense of an elder day is the common nonsense of our own." "The history of human opinions," said Voltaire, "is scarcely anything more than the history of human errors."