44 Motion of a System of Bodies. 
whether we invert the motion of the plate or make the magnet re- 
volve in opposite directions. 
When the magnet is suspended directly over the centre of the re- 
volving plate, (and which is called its concentric position,) it receives 
no impulse; because the voltaic currents thus generated, lie in planes 
passing through the magnetic axis of N, and those of the same de- 
nomination meet at the centre. ‘The counter currents that thus arise 
upon opposite sides of the magnetic pole, exactly neutralize each other. 
Art. IV.—Motion of a System of Bodies ; 
by Prof. THEoporr Strong. 
Continued from Vol. xxv, p. 289. 
Again, supposing 'T’, ‘I’, &c. to denote the same things as before, 
we have Qz - Py= (2 xQ== xP jr=Tr, for - X Q= the force Q 
when resolved at right angles to 7, and z <x P= the force P resolved 
eral a) 
Ws igs 
© 1 
at right angles to r, and ~ xQ-2 ake = the resultant of | 
the forces = XQ,” xP, since they act in contrary directions; in the 
d?y— yd? x, 
same way eee and so on; hence we have it aN 
ad? / ‘d2x : 
07, —— =Tr, &c.; .".it may be shown in the very 
same way as at p. 43, that if we multiply these equations by m, m’, 
&c. respectively, we shall have, (by adding the products,) the equa- 
cd? y — yd? 
tion aa | =SmT’r, which is independent of the recipro- 
cal actions of the bodies m, m’, &c.; by restoring the values of Tr, 
Tr’, &c. we have the first of (18); and ina similar way may. the se- 
cond and third be found. Let h denote the distance of m from the 
origin of the coordinates, then if m is acted upon by any force mF in 
the direction of the straight line h, we Snes have F for the force which 
acts on a unit of m in that direction; .’. by resolving F in the direc- 
tions of the axes of x and y, we have EXE: AXE for the parts of P 
and Q respectively which arise from F’, .*. by considering these forces 
