In our Mechanics' Fair, there must be not only bridges, ploughs, carpenter's planes, and baking troughs, but also some few finer instruments,--rain-gauges, thermometers, and telescopes; and in society, besides farmers, sailors, and weavers, there must be a few persons of purer fire kept specially as gauges and meters of character; persons of a fine, detecting instinct, who note the smallest accumulations of wit and feeling in the bystander.