132 Mr. E. Hunt on certain Phenomena connected with 



action, due to the disturbed equilibrium of the centrifugal forces, pla^-s 

 an important part in the complete explanation of the gyroscope pheno- 

 mena ; indeed, without it, the gyroscope, or the weight acting on it, 

 would not, under ordinary conditions, move horizontally. 



The gyroscope, almost in its present common form, was invented by 

 Hen* Fessel about six years ago, and is represented and described in 

 Poggendorff's Annals for 1853. He was making a small fly-wheel for 

 a model steam engine, and was spinning it in his hands to see if it was 

 true, when he felt an extraordinary apparent resistance to any angular 

 movement of the spindle, and also found that it did not fall when 

 supported only on one side. A slightly diiFerent apparatus, showing 

 similar phenomena, was invented as long ago as 1810 or eai-lier, by 

 Bohnenberger, and is represented and described in Gilba-f's Annals for 

 1818.* I now exhibit a common gyroscope, and some apparatus which 

 can be adjusted to act either as a Bohnenberger gyroscope, or as a 

 Fessel gyroscope, and which can be made to show a great variety of 

 curious and interesting phenomena. 



In the Bohnenberger apparatus, a spheroid or fly-wheel is set on pivots 

 in a ring, with its spindle in a diametrical position. At points a 

 quai-ter round from the fly-wheel pivots, this first ring is supported on 

 pivots within a second ring, which is capable of turning about a vertical 

 axis on pivots fixed on the stationaiy part of the apparatus. The axis 

 about wliich the fly-wheel and rings severally turn, all pass through the 

 central point of the apparatus, which ought also to be the common centre 

 of gravity, so that the fly-wheel may be said to be siipported at this 

 point, whilst any iucHnation whatever may be given to its spindle. If 

 the fly-wheel be set spinning, with its spindle in any but a vertical 

 position, and a weight be applied to one end of the spindle, the weight 

 will not bring that end of the spindle down as might at first be expected, 

 but will be carried round in a horizontal plane. The Fessel gyroscope, 

 as now constructed, consists of a flj'-wheel set on pivots in a ring, a 

 small conical indentation being formed in a prolongation of the sjiindle, 

 so that when the ring is set with this indentation upon the pointed top 

 of a pillar, it can turn round this point horizontally, and to a certain 

 extent, vertically. The point of support is all to one side, and when 

 the fly-wheel is not spinning the gyroscope falls down against the pillar. 

 When, however, the fly-wheel is set spinning, the gj-roscope does not 



* Since this paper was written, I have seen in Silliman's American Journal for 1832, 

 the description of a " Rotascope," designed by Prof W. R. Johnston of the Franklin 

 Institute, for exhibiting various experiments with rotating bodies. One of the experi- 

 ments described is the same as the Fessel experiment, so lliat both Foucault and Fessel 

 were anticipated as regards it. 



