  Dark Energy is currently one of the biggest mysteries in science. In this
article the origin of the concept is traced as far back as Newton and Hooke in
the seventeenth century. Newton considered, along with the inverse square law,
a force of attraction that varies linearly with distance. A direct link can be
made between this term and Einstein's cosmological constant, Lambda, and this
leads to a possible relation between Lambda and the total mass of the universe.
Mach's influence on Einstein is discussed and the convoluted history of Lambda
throughout the last ninety years is coherently presented.
