Bifocals are eyeglasses with an upper and lower half, the upper for distance, and the lower for reading. Bifocals are commonly prescribed to people with presbyopia, a condition that Franklin suffered. Franklin wrote, in August 1784 to his friend George Whatley, that he was "happy in the invention of double spectacles, which serving for distant objects as well as near ones, make my eyes as useful to me as ever they were."
Once Franklin had an understanding of the behavior of electricity, he set about to protect houses from the destructive forces of lightning. A lightning rod, simply, is a rod attached to the top of a building, connected to the ground through a wire. The electric charge from lightning strikes the rod and the charge is conducted harmlessly into the ground. This protects houses from burning down and people from electrocution.
In colonial America, homes were warmed by a fireplace. The Franklin stove, invented in 1742, is a metal-lined fireplace that stands in the middle of a room. It has rear baffles for improved airflow. It provides more heat and less smoke than an open fireplace and uses less wood. This cast-iron furnace would radiate heat from the middle of the room in all directions, and the iron walls even absorbed heat, providing warmth to the room long after the fire went out.
Benjamin Franklin was an avid swimmer from a very young age. Throughout his life he consistently promoted its healthful benefits. At the ripe old age of 11 he invented a pair of swim fins. However, unlike today's foot flippers, these were attached to one's hands. His advocacy for swimming was recognized by his induction into the International Swimming Hall of Fame in 1968.
Franklin was curious as to how far he was traveling by carriage, in his role as postmaster, for his travels between Philadelphia and Boston. While the concept of the odometer dates back to ancient times, Franklin did create his...