Between 1995 and 1999 the ATOC, or Acoustical Thermometry of Ocean Climate, experiments measured the speed of sound in the Pacific Ocean. Sound sources at 75 hertz were located off the California coast and near the island of Kuaui in Hawaii. Detectors were positioned at various depths off the coast of Alaska, near the Big Island of Hawaii, near Kamchatka, Russia, and New Zealand. The waves took up to an hour to travel these large distances and the system was able to find the time of travel to under 0.02 seconds, so extremely accurate measurements of the speed of sound could be made. The speed of sound in saltwater depends only slightly on the degree of salinity, but increases 6.4 meters per second for every degree Celsius increase in temperature. They were able to measure the water temperature to within 0.01°F.

In the 1660s, English scientist Robert Boyle (1627–1691) proved that sound waves need to travel through a medium in order to transmit sound. Boyle placed a bell inside a vacuum and showed that as the air was evacuated from the chamber, the sound of the bell became softer and softer, until there was no sound.