The method of scientific investigation is nothing but the expression of the necessary mode of working of the human mind; it is simply the mode by which all phenomena are reasoned about and given precise and exact explanation. There is no more difference, but there is just the same kind of difference, between the mental operations of a man of science and those of an ordinary person., as there is between the operations and methods of a baker or of a butcher weighing out his goods in common scales, and the operations of a chemist in performing a difficult and complex analysis by means of his balance and finely graded weights. It is not that the scales in the one case, and the balance in other, differ in the principles of their construction or manner of working; but that the latter is a much finer apparatus and of course much more accurate in its measurement than the former.
