The construction of a versatile viscometer of coaxial cylinder type is described. The apparatus can be used (i) not only as a viscometer by hanging a weight on a pulley attached to the inner cylinder and observing its rotation velocity or by rotating the outer cylinder uniformly and measuring the torque exerted on the inner cylinder, (ii) but also as a viscoelastometer by setting the outer cylinder in rotatory oscillation and recording optically the oscillatory motion of the inner cylinder,

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... enabling us to evaluate the amplitude ratio and phase difference between these two motions and therefrom the dynamic viscosity and rigidity of a specimen in a frequency range up to 10 cps. Some results of preliminary measurements on silicone oils are presented as examples.