The experiments here described, which were made during April and May of the present year (1888), to determine the constant of viscosity of water, may be of some interest on account of the newness of the method employed, and also as being on rather a larger scale than other experiments which have been made with the same object. Fig. 1 gives a section of the apparatus used. A and B are two coaxial cylinders; of these A is mounted on the vertical axis E, and can be made to rotate by a belt passing over the wheel F. B is suspended by a long fine wire C, and the annular space between A and B is filled with water or any other fluid to be experimented on.