120 PROCEEDINGS OF THE AMERICAN ACADEMY. 



seat. The nut K locks the adjustment of the bearing at the proper 

 height. The lateral bearings A and H as well as the top bearing 

 of the turbine itself, consist of eminently satisfactory graphite-lined 

 bushings supplied by the Graphite Lubricating Co., Bound Brook, 

 N. J. The lubrication of the ball bearings was also with graphite 

 which was applied with oil in the form of a paste. 



This form of ball bearing was tried only after a number of bearings, 

 including one specially designed for the purpose by The Standard 

 Roller Bearing Co., had failed. The individual ball bearings of which 

 this bearing was constructed were stock 13/16 inch " ball thrust collar " 

 bearings made by the above firm. The ingenious idea of replacing 

 the series of disks sometimes used in step bearings by a series of ball 

 bearings came in a conversation with Dr. C. A. Kraus of this labora- 

 tory, to whom, in general, I am under the deepest obligation for an 

 intelligent and sympathetic understanding of the many di^iculties 

 involved in the construction of an apparatus of this kind. 



The ^^ Spinning Top." 



The rotator B, Figure 1, is two feet in diameter and consists of two 

 hollow steel arms, screwed into a central hub P. The rotator is hung 

 on a" shaft 13/16 inch diameter and 8-1/2 inches long. This shaft is 

 flexibly connected to the turbine shaft with a Hooke joint M, which 

 permits the rotator to revolve about its own center of gravity. The 

 arrangement is in the nature of a "spinning top." In order to pre- 

 vent a precessional motion of the top which would quickly raise the 

 rotator shaft to a horizontal position, the shaft was steadied at the 

 point N by a system of cords not shown in Figure 1, but indicated in 

 plan in Figure 3. The two cords MN and OP prevent motion of the 

 shaft in the direction AA, and two others not shown in the figure are 

 arranged to prevent motion in the direction BB. The cords were 

 drawn tight against the shaft through the stationary supports at W, X, 

 Y, and Z. The cords were braided cotton 5/32 inch in diameter and 

 the wear on them, strange as it may seem, was very inconsiderable. 

 This arrangement of cords was adopted after experimenting with many 

 forms of steadying bearing, in which it was attempted to prevent the 

 precessional motion with rubber washers, springs, or pneumatic dash 

 pots. 



This plan of driving the rotator as a spinning top must be consid- 

 ered as one of the distinctive features of the apparatus. • By this 

 means the rotator was driven up to a speed of 7850 revolutions per 

 minute, giving a rim speed of nearly 50,000 feet per minute. At this 



