"They commence by gathering at one point, then they describe a series of circles around this point, at first very small, but whose circumference enlarges at every sweep.
"Little by little the central point is abandoned, they no longer approach it, and disappear in the sky, drawn by their fancy toward another point which they will leave very soon.
"The thoughts of one who does not know how to gather them together and to concentrate them are like these birds.
"They start from a central point, then spread out, at first without getting far from this center, but soon they lose sight of it and fly toward a totally different subject that a mental representation has just produced.
"And this lasts until the moment when, in a sudden movement, the first one is conscious of this wandering tendency.
"But it is often too late to bring back these wanderers to the initial idea, for, in the course of their circuits, they have brushed against a hundred others, which are confounded with the first, weaken it, and take away its exact proportions.
"The great stumbling-block again is that of becoming lost in the details whose multiplicity prevents us from discerning their complete function in the act of practising deduction.
"It is better, in the case where our perception finds itself assailed by the multitude of these details, to proceed by the process of elimination, in order not to become involved in useless and lazy efforts.
"In this case we must act like a man who must determine the color of a material at a distance where the tiny designs stand out in a relief of white on a background of black.
"Suppose that he is placed at a distance too great to perceive this detail.