OF ARTS AND SCIENCES. 



207 



no peculiar virtue; which does not direct the mind, but which the 

 mind must direct lil;e any other instrument.' 



" The origin of FessePs machine was as follows. About 1851 

 this skilful artist of Cologne, who a few years before had distin- 

 guished himself by his beautiful Wave-machine, particularly adapted 

 for iUustrating the mechanical laws of light, was examining the wheel 

 of a model steam-engine, and observed that, while rolling it on his 

 hand, the horizontal axis did not require to be supported at both ends, 

 while there was a tendency in the axis to move in a horizontal plane. 

 Fessel's practical skill, aided by the suggestions of the eminent physi- 

 cist Pliicker, resulted in the construction of the following apparatus. 



The wood-cut represents the apparatus, not exactly as figured in the 

 Annalen of Poggendorf, but as constructed by Luhme, and now ex- 

 hibited. It is about half the size of the model. Upon a heavy base, 

 A, stands a hollow brass column, B, inside of which turns a steel pin, 

 C, terminating at the lower end in a point. At right angles to this pin 

 are fastened the metallic arms D D. On one of these arms, and at the 

 distance of two inches from the pin, is fastened a vertical ring. Inside 

 of this ring is placed a metallic disc, E, loaded at the edge ; and which 

 turns, independently of the ring, upon the axis F G. The motion is 

 communicated by a thread wound upon the axis of the disc. At h is 



