92 



elaborate one was contrived by Prof. Walter R. Johnson, of 

 Philadelphia, and hj him illustrated in the Journal of Science, 

 in the year 1832. And the well known and similar apparatus 

 of Bohnenberger, was described in scientific journals as far 

 back as 1817. But since about the year 1851 the apparatus 

 has received much attention and improvement from various 

 physicists, as Foucault, Magnus, Wheatstone, and others in 

 Europe ; and in our own country, it has becom_e a household toy ; 

 many thousands of them, having been sold during the last year. 



The principles upon which it operates have been thoroughly 

 discuss''d in various works on Dynamics — among which, is the 

 very lucid analytical investigations, contained in the fourth 

 chapter of the second part of Poisson's Treatise on Mechanics. 



The principles of the action of the common humming top 

 were analytically discussed in the second number of the Cam- 

 bridge Miscellany, a mathematical journal published July. 

 1842, at Cambridge, Mass. — edited by Professors Peirce and 

 Levering. 



I will endeavor to elucidate the actions of the forces which 

 sustain the motions of the instrument before us. 



It is one of the fundamental laws of rotary motion, that if 

 motions of rotation are impressed on a body, causing it to 

 revolve at the same time around two different axes inclined to 

 each other — the body will tend to revolve about an axis situated 

 between the two, and inclined nearest to the direction of that 

 axis about which exists, for the time being, the most rapid 

 rotation. If, without impressing any rotation upon the wheel, 

 I place the ear of the ring upon the point of the stand and 

 abandon the apparatus to itself, it falls to the table as might 

 have been expected. If now. on the contrary, I wind this 

 string upon the axis of the wheel, and holding the ring firmly 

 in one hand, with the other rapidly unrolling the string, a great 

 velocity will be communicated to the wheel, and the force 

 which I expended in pulling the string, is treasured up in the 

 momentum of the wheel. 



Let us now place the ear of the ring upon the central 

 pivot and abandoning the system to itself await the results ; 

 instead of falling, as it did before, when the wheel is not rotat- 

 ing, it commences to revolve around the vertical pivot which 



