<div class="htmlview paragraph"><b>THE theory of the untuned viscous damper is developed mathematically here by Mr. O'Connor to show that its characteristics are such as to make practical the use of silicone fluid as a damping medium.</b></div> <div class="htmlview paragraph"><b>That this type of damper achieves a high relative efficiency throughout a wide range of damping is indicated by a consideration of a simple mass system. The performance of a damper applied to the mass elastic system of a typical 6-cyl gasoline engine is predicted to be satisfactory over a range of speeds and values of the damping constant.</b></div> <div class="htmlview paragraph"><b>An exact tabular method and a simpler approximate method are proposed for calculating the maximum amplitude and the frequency at which it occurs. The approximate value of optimum damping can also be found by a simple procedure.</b></div>