NATURAL PHILOSOPHY. 181 



the hand was taken from it. But, upon imparting to it rapid rotatory 

 motion, it stood up even beyond the horizontal position, so as to hring its 

 axis of rotation nearly to the same inclination to the horizon as the axis 

 of the earth, while the whole acquired a slow rotatory motion round the 

 point of the hook ; and so steady was its equilibrium while moving thus, 

 that a string being passed under the hook, and both ends brought together 

 in the hand, the whole may be lifted by the cord off the stand and carried 

 revolving steadily about the room. Next, to show the motion of the earth 

 sensibly, he placed the gymbai gyroscope, suspended freely by a fine silk 

 fibre, in a stand, with the lower steel point of its support resting in an 

 agate cup ; a long light pointer projecting from the ring carried a pointed 

 card, which passed over a graduated card arch of a circle placed concentri- 

 cally with the gyroscope ; upon imparting rapid rotatory motion to the 

 gyroscope, the index was seen as the earth moved to point out the relative 

 motion of the plane of rotation exactly in the same way : the law of the 

 motion being also the same as that of the well-known pendulum experi- 

 ment. Lastly, he set the ring gyroscope in motion, and by placing a 

 small pointed piece of brass at the end of the axle on the ring, the instru- 

 ment went immediately through all the evolutions of a boy's top on the 

 floor, humming meanwhile loudly also. 



These beautiful and most decisive experiments were received most 

 enthusiastically. 



OX CERTAIN PHENOMENA OF ROTATORY MOTION. 



The following is an abstract of a lecture delivered before the Royal 

 Institution, London, by Professor Baden Powell, on the above subject, 

 which has excited considerable attention, on account of the novelty and 

 interest of the views and experiments alluded to. The mechanical 

 principle of " the composition of Rotatory Motion," originally discovered 

 by Frisi about 1750, is equally simple in its nature, important and fertile 

 in its consequences and applications, and susceptible of the easiest explana- 

 tion and experimental illustration ; yet it has been singularly lost sight of 

 in the common elementary treatises. The principle is involved in the 

 explanation of several important phenomena, some of which are in fact 

 mere direct instances of it, so that a simple experimental mode of exhibit- 

 ing it would be eminently desirable ; and several such have accordingly 

 been devised, which yet seem to have been but little generally known. 

 Such an apparatus, designed for lecture illustration, had been constructed 

 by the author, the object of which was to show experimentally, without 

 the use of complex and delicate machinery, the actual composition of 

 rotations about two different axes impressed at once on the same body. 

 The essential parts are merely a bar capable of rotating freely about one 

 end of an axis, (and loaded at its extremities to keep up the rotation,) 

 while the ax-is itself can turn about a point in its length, near the end 

 carrying the bar, upon a horizontal axis, capable of moving freely round a 



