This invention relates to methods and apparatus for investigating the composition of material.
More particularly the invention relates to such methods and apparatus for use in determining the proportions of different components in a material, more specifically in fluid form, flowing along a closed duct, such as a pipe, without physically interfering with the wall of the duct. One particular example of such a use is the investigation of the relative proportions of oil and water in material obtained from a sub-sea oil well.