References 1 D. M. Smith, "The Motion of a Rotor Carried by a Flexible Shaft in Flexible Bearings, " Proceedings of The Royal Society, series

The author is to be congratulated on the report of the study he has made in the field of whirl phenomena. The method of presentation is extremely meritorious, particularly the explana-tion of the mechanics of backward and forward whirl. The "flat shaft " discussion, in particular, could well be included in texts on the subject of vibration where ordinarily only brief mention is made. The author has used both an intentional out-of-balance weight, a flattened shaft, and a combination of the two as the exciting element for whirl. He has further introduced asymmetric bearing stiffness in the form of outboard springs. Under the foregoing conditions, he has achieved backward whirl in Case I, only be-tween the horizontal critical and the vertical criticals. Case II yielded only forward whirl. In Case III, a combination of I and II, backward whirl has again been encountered only between th