Colour engraving by Josiah Wood Whymper showing men using poles to break up ice floes, with a ship trying to navigate the tightly packed ice in the distance. 'Sea water requires a much greater degree of cold to freeze it than fresh water, and the motion of the waves interferes with the formation of solid ice. Under certain conditions, however, 'fields' of ice can be formed, often extending to a distance of several hundred square miles. When warmer weather prevails, these fields can be broken into smaller pieces of ice which are called 'floes'.' Illustration from 'Phenomena of Nature', published in London in 1849 for the Society for Promoting Christian Knowledge.
© Science Museum / Science & Society Picture Library