Rotational viscometers

A rotational viscometer consisting of a first member and a second member, relatively rotatable about a common vertical axis, the member between them defining a cavity for the reception of a fluid under test, means for rotating the first member, a permanent magnet arranged within the second member and on the said axis, a second permanent magnet arranged on the said axis adjacent the first magnet, the arrangement being such that the magnets interact to maintain the members coaxial during rotation of the first member, said first member being a hollow vertically extending cylinder open at its upper end defining within it a cavity for the reception of a fluid to be tested, said cavity having a floor of electrically non-conductive material, and said second member being a cylinder arranged within the said cavity, the permanent magnet arranged within said second member tapering to a point on the said axis at its lower end, the second magnet being supported immediately below the floor of the said cavity, the upper end thereof being tapered to a point lying on said axis.