206 PROCEEDINGS OF THE AMERICAN ACADEMY 



Professor Joseph Lovering asked the attention of the Acad- 

 emy to the following remarks on motions of rotation. 



" Since the time of Foucault's celebrated experiment for illus- 

 trating the rotation of the earth by the stability of the plane of 

 oscillation, increased attention has been given to the law of inertia 

 as determining the stability of planes of motion. The planes o( rota- 

 tion conform to this general rule of stability. Astronomy furnishes 

 the only examples of perfectly free rotating bodies: and astronomy, 

 here, as elsewhere, must be invoked, whenever it is required to give 

 an exact experimental illustration of the fundamental laws of mechan- 

 ics. Artificial experiments realize but imperfectly this perfect free- 

 dom of the spinning earth and other planets. Besides the top and the 

 devil-on-two-sticks, in which ' philosophy in sport has been made 

 science in earnest,' there are Bohnenberger's less familiar apparatus, 

 first described in 1817,* and Johnston's Rotascope.t The necessity 

 has recently been shown of adding to the description of the former 

 the r\e\v condition of placing the axis of the apparatus parallel to the 

 earth's axis to avoid the disturbance of the earth's rotation, and the 

 new application of the instrument, when otherwise placed, to detecting 

 this rotation, t 



" In 1853, Pliicker published an account of Fessel's apparatus for 

 experiments on the laws of rotation ; "^ and in 1854, Magnus pre- 

 sented to the public an account of his Polytrop, also designed for 

 similar illustrations. || 



" 1. Pliicker preludes his description of the Fessel machine with 

 some remarks on Poisson's mathematical investigations on the subject 

 of rotations,^ and alludes to Poinset's successful attempt to make the 

 motions generally hidden under the veil of mathematical analysis 

 more sensible to the imagination and the eye.** Poinset thinks t' at, 

 if many new truths are contained in analysis, they are buried in it for 

 all but a ie\w gifted minds. ' Thus our true method is but this happy 

 mixture of analysis and synthesis, where calculation is employed only 

 as an instrument, a precious instrument, and necessary without doubt, 

 because it assures and facilitates our progress ; but which has of itself 



* Ann. Gilbert, LX. p. 05. t SiHiman's Journal, XXI. p. 265. 



\ Ann. Pogg., XC. pp. 350, 351. § Ann. Pogg., XC. p. 174. 



II Ann. Pogg., XCI. p. 298. 1 Journ. de Polytechn. Ecole, XVI. p. 247. 



** Elemens de Statique, 8th edition, 1842. 



