The stone in the belly – focus and weight – where a quiet disciplined mind wants to settle, should more appropriately be called the plumb in the belly. That small ball of lead better suits the essential nature of dantien – its feeling of concentrated essence – its density and mass always pulling the spine into verticality. Taoism is heavily influenced by Chinese alchemy – the art of extracting essence from substance, from things. Imagine the early chemists' amazement when they discovered that when certain rocks from the Earth were crushed and heated very hot, a trickle of dense shiny liquid appeared which cooled into metal with all its remarkable qualities, not least its ability to be fashioned into jewellery and weaponry. The very concept of essence – the idea that things have an essential nature somehow independent of external character and form – is the foundation of our concept of the Internal.