Reconstruction of thermoscope for measuring temperatures in the ocean, from a design by Robert Hooke c.1690, made by the Science Museum, London, UK 1977.

The early Royal Society of London (founded 1660) encouraged marine science, and Curator of Experiments Robert Hooke (1635-1703) devised various instruments for studying and observing the ocean. Some of his designs were constructed but were only tested in the calm waters of the river where he demonstrated them to the society.

The thermoscope had a globe filled with spirits of wine. The inner glass tube had a valve at its bottom end, though this is not shown on Hooke’s drawing or in this reconstructed instrument. On being lowered into cold water the spirits of wine contracted, drawing down the inner tube. When the thermometer was hauled in, the expanding spirit passed through the valve up into the inner tube. The length between the inner and outer tubes was therefore a measure of the difference in temperature at the surface and at the depth to which the instrument had been lowered. In practice, such an instrument would have been affected far more by pressure than by temperature.