A Matter of Equilibrium

I climbed onto the wooden surface of the coffee table. Near the edge lay a wooden ruler and three smooth dominoes. I set the first domino upright. Its flat base met the grain with an audible click. I placed the ruler across its narrow top edge. The wooden slat tilted, sliding downward. I adjusted the pivot point three millimeters to the right. The seesaw leveled. Next, I balanced an empty glass marble on the far end. My fingers pressed lightly against the rim. The entire structure trembled, then settled into stillness. A perfect horizontal line.