That small word “Force,” they make a barber's block, Ready to put on Meanings most strange and various, fit to shock Pupils of .... The phrases of last century in this Linger to play tricks— Vis viva and Vis Mortua and Vis Acceleratrix:— Those long-nebbed words that to our text books still Cling by their titles, And from them creep, as entozoa will, Into our vitals. But see! Tait writes in lucid symbols clear One small equation; And Force becomes of Energy a mere Space-variation.