The normal man, on the other hand, has only a single intellect, which may be called _subjective_ by contrast with the _objective_ intellect of genius. However acute this subjective intellect may be--and it exists in very various degrees of perfection--it is never on the same level with the double intellect of genius; just as the open chest notes of the human voice, however high, are essentially different from the falsetto notes. These, like the two upper octaves of the flute and the harmonics of the violin, are produced by the column of air dividing itself into two vibrating halves, with a node between them; while the open chest notes of the human voice and the lower octave of the flute are produced by the undivided column of air vibrating as a whole. This illustration may help the reader to understand that specific peculiarity of genius which is unmistakably stamped on the works, and even on the physiognomy, of him who is gifted with it. At the same time it is obvious that a double intellect like this must, as a rule, obstruct the service of the will; and this explains the poor capacity often shown by genius in the conduct of life. And what specially characterizes genius is that it has none of that sobriety of temper which is always to be found in the ordinary simple intellect, be it acute or dull. The brain may be likened to a parasite which is nourished as a part of the human frame without contributing directly to its inner economy; it is securely housed in the topmost story, and there leads a self-sufficient and independent life. In the same way it may be said that a man endowed with great mental gifts leads, apart from the individual life common to all, a second life, purely of the intellect. He devotes himself to the constant increase, rectification and extension, not of mere learning, but of real systematic knowledge and insight; and remains untouched by the fate that overtakes him personally, so long as it does not disturb him in his work. It is thus a life which raises a man and sets him above fate and its changes. Always thinking, learning, experimenting, practicing his knowledge, the man soon comes to look upon this second life as the chief mode of existence, and his merely personal life as something subordinate, serving only to advance ends higher than itself.