394 NOTICES OF THE MEETINGS [March 3, 
308). These, however, are not books of a popular kind, and the 
author is not aware of any mention of it in other English works. 
In a more abstract analytical form it has been discussed by several 
foreign mathematicians, especially by Poinsot, in a Memoir read to 
the Academy of Sciences, May 19, 1834, but of which only an 
abstract was published; as well as by Poisson, in a paper in the 
Journal de l’Ecole Polytechnique (xvi. 247). 
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 exhibiting it would be emi- 
nently desirable; and several such have accordingly been devised 
which yet seem to have been but little generally known. 
An ingenious instrument of the kind was contrived some years 
ago by Mr. H. Atkinson, a very brief account of which is given in the 
Astronomical Society’s Notices, vol. i. p. 43, though so brief that 
it is difficult to collect what the precise mode of its action was,— 
but it seems somewhat complex. 
A far more complete and instructive apparatus was invented by 
Bonenberger and described in Gilbert’s Annalen (Ix. p. 60). It is 
also explained in some German elementary works. Attention has 
been more recently drawn to the subject by a highly interesting 
paper of Professor Magnus of Berlin, (Abhandlungen der Konig]. 
Preuss. Akad. 1852, translated in Taylor’s Foreign Scientific Memoirs, 
N. S. Part 3, p. 210,) in which some remarkable applications of this 
apparatus are given; he also describes it (with a figure) and observes 
that the execution of it requires great delicacy and correctness of 
workmanship. Copies of this instrument have indeed been made in 
this country (one of which was exhibited through the kindness of Pro- 
fessor Wheatstone); but of these the author believes no description 
has ever appeared in English works, and they are certainly very little 
known, notwithstanding their manifest value to every lecturer: the 
essential parts are a sphere capable of rotating about an axis whose 
extremities rest in opposite points of a hoop which can turn on 
pivots horizontally, within another hoop turning on pivots about a 
vertical line. 
In fact the author of the present communication has long felt 
the want of such an apparatus for lecture illustration; and before he 
was aware of the existence of any of those just alluded to, had con- 
structed one in a different form, and which is found to answer fully 
the purposes of illustration for which it is designed, without any nice 
workmanship or complex machinery. (See Astronomical Society’s 
Notices, vol. xiii. p. 221-248.) 
Its object, like that of the instrument last mentioned, is to exhibit 
experimentally 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 axis itself can turn about a point in its 
