Currents, both in air and water, have played a substantial role in human transportation and travel over the years. In the 1700s Benjamin Franklin was the deputy postmaster general for the North American colonies. Franklin noted that the mail took longer to arrive from England to the colonies than it took to send mail from the colonies back east to England. He convinced his nephew Timothy Folger, a whaling ship captain who traveled between England and the colonies, to conduct a simple experiment. Folger dropped bottles over the side of his ship and noted how fast they were moving and in which direction. Franklin also took several trips in which he measured the temperature of the water and air, knowing that water in the Gulf Stream (SF Fig. 3.4), which was traveling from warmer southern waters, would be warmer. Franklin and Folger were able to produce the first maps of the Gulf Stream. They described a fast moving current or “underwater river” that flows up the east coast of North America.