(b) The formula for centripetal acceleration – and the concept of such acceleration itself – is the result of splitting circular movement into two rectilinear movements, one in the direction of the tangent, the other in the direction of the radius, and of regarding it – by a mode of reasoning typical of spectator-thinking – as composed of the two. This procedure, however, useful as it may be for the purpose of calculation, is contrary to observation. For, as we have pointed out earlier, observation tells us that all original movement – and what can be more original than the movements of the planetary bodies – is curvilinear. No insight into the dynamic reality of cosmic movement, therefore, can ever be gained by handling it mathematically in this way.