In 1826, Jean-Daniel Colladen, a Swiss physicist/engineer and Charles-Francois Sturm, a mathematician, used an underwater bell in an attempt to calculate the speed of sound in the waters of Lake Geneva, Switzerland . In his experiment an underwater bell was struck simultaneously with ignition of gunpowder. The flash from the ignition was observed 10 miles away and compared with the arrival of the sound from the bell underwater heard through a trumpet-like device in the water. In spite of these crude instruments, they managed to determine that the speed of sound under water was 1435 metres/second, a figure not too different from what is known today.
Image courtesy of The Marine Group