Although that might well be so, there is a motion nevertheless of which the equation is a (this is Kepler's law of the motion of the bodies of the solar etc., system), and what the meaning here of the first derived function, a might be, and the further direct manipulation of this equation by differentiation, the development of the laws and the determinations of the absolute motion from this starting point all this must on the contrary appear indeed as an interesting problem, an opportunity for analysis to display its worth at its most brilliant.