594 



NATURE 



magnet can be placed in any azimuthal position which 

 may be required. The galvanometric frame has been so 

 constructed that the the horseshoe-magnet may be taken 

 away and be replaced by any number of bar-magnets 

 laid flat upon its upper side. It is possible also to 



{April 2 2, 1 8 So 



place other bar-magnets underneath the frame in a space 

 arranged for that purpose, or to place the two magnets 

 laterally, or on the left and right side of the frame 

 (Fig. 2). 

 To produce a continuous movement of rotation with 



R/X. 



Fig. i. — Some of the soft iron rotators used in the gyroscope. 



the intervention of the" magnets it is sufficient to place the velocity is observed when we place the bar-magnets 

 any movable piece of iron in equilibrium by means of a i underneath which have been originally placed on the top, 

 block on a vertical axis (Fig. 3) inside of the frame, and ■ or vice versd. If the magnets are too near or too far 

 to send the current of induction into the coil. When, by from the rotating piece of iron, the motion ceases, which, 



I under favourable circumstances, might acquire a very 

 1 great velocity. The rotation is also stopped when the 

 magnets are placed in a direction perpendicular to the 

 frame. 



The movable piece may be placed also at a small dis- 

 tance laterally without the rotation ceasing to take place. 

 It may be also placed on the top, and be rotated by the 

 influence of the bar magnets placed underneath. 



The same phenomena may be obtained very easily with 

 a bar electro-magnet of which one pole is presented at a 

 distance of several metres. In this case the experi- 



*A*h 



Fig. 3. — Movable piece balanced on its axis, ready 

 the galvanometric frame. 



be introduced into 



Fig. 2. — Rotating induction machine surmounted by a magnet. The 

 operator is introducing a magnet into the space underneath the frame 



means of a commutator, the direction of the primary is 

 changed, the direction of the motion of rotation is re- 

 versed. The same phenomenon is observed when we 

 transfer the poles of the acting magnets from left to 

 right, or vice versa. But no sensible alteration even in 



ment is very curious, and looks like a conjuring trick, 

 as two or three movables can be rotated at once. 

 A mere change in the pole presented produces a change 

 in the direction of rotation as well as the displace- 

 ment from one side of the axis to another. But the 

 operator must be careful not to approach too near, other- 

 wise, the power of the electro-magnet b;ing too great, the 

 action of the induction-current is absorbed, and no 

 motion at all is observed. If the operator is quite near, 

 the movable pieces of iron are attracted magnetically, and 

 fly from the pivots where they have been rotating, to 

 the pole of the electro-magnet. To ascertain the velocity 

 of the movable pieces of iron it is advisable to have them 

 painted half in white and half in black, so thlt they 



