A New Form of Rotator. By Leroy C. Cooley, Ph. D. 



[Read before the Albany Institute, April 1, 1873]. 



Rotary motion is of vital importance as a means of 

 developing principles in physics. Optical, electrical, 

 acoustic and magnetic experiments, to say nothiug of the 

 numerous well known illustrations of the " Central forces " 

 constitute a series of important demonstrations of great 

 beauty and variety. Until the present, no instrument has 

 had capacity to grasp the necessary conditions of all cases, 

 and consequently various forms of whirling table or ro- 

 tator, each adapted to special experiments, have been 

 devised. 



But notwithstanding their great variety the experiments 

 in rotary motion may, for the most part, be grouped in 

 three classes, viz : First, those in which the rotating body 

 must be firmly attached to a vertical axis : second, those in 

 which the rotating body must be freely suspended from a 

 vertical axis, and third, those like the Geisler tubes and 

 optical disks, in which the rotating body must be firmly 

 attached to a horizontal axis. 



To adapt a single instrument to these three classes of 

 experiment, it is only necessary to utilize both ends of the 

 axis of the pulley and to be able at a moment's notice to 

 shift the axis itself from a vertical to a horizontal position. 



This has been accomplished as follows : — From the 

 centre of a base of convenient size a single column rises 

 to a height of about two feet. Across the top of this col- 

 umn, and firmly fixed upon it, is a table measuring about 

 twenty inches in length by five in width. Upon this table 

 and fastened to it by hinges is a strong bar of wood, two and 



