The true origins of the BT began in 1935 when Carl-Gustaf Rossby started experimenting. He then forwarded the development of the BT to his graduate student Athelstan Spilhaus, who then fully developed the BT in 1938 as a collaboration between MIT, Woods Hole Oceanographic Institution (WHOI), and the U.S. Navy. The device was modified during World War II to gather information on the varying temperature of the ocean for the U.S. Navy. Originally the slides were prepared "by rubbing a bit of skunk oil on with a finger and then wiping off with the soft side of one's hand,” followed by smoking the slide over the flame of a Bunsen burner. Later on the skunk oil was replace with an evaporated metal film.