Description of the Rotascope. 267 



vary the relative position of its poles ; bat if the globe receive a 

 rapid rotary motion, previously to the commencement of its oscilla- 

 tions, there will be a vigorous effort visible at every oscillation, tend- 

 ing to alter the direction of the axis of the globe. 



A little observation will serve to ascertain, that the position which 

 the axis affects, is such as to bring the rotary motion referred to the 

 centre of the sphere into the same plane and the same direction as 

 that of the oscillation, referring the latter to the centre or point of 

 suspension of the pendulum. Hence, if we watch the motion of the 

 exterior of the globe, we shall perceive that the rising side in the 

 rotation, is the anteiior side in the oscillation, and that the inverting 

 takes place, the instant the pendulum begins to descend in the aiq, of 

 oscillation. 



3. There is in use a small apparatus for striking fire, composed of 

 a semi-cylindrical box of tinned iron a kw inches in length, at one 

 end of which is a small cavity for receiving the tinder, and above it 

 is mounted on an axis a disk of steel to strike, when in rapid motion, 

 upon a flint, held just above the tinder. The steel disk is put in mo- 

 tion by the friction of a string, drawn briskly over a small pulley on 

 the axis. If, when the vi'heel, which is about two inches in diame- 

 ter, is revolving vertically, we hold the whole loosely in the hand ex- 

 tended, and carry the latter alternately right and left before the body, 

 so as to cause the wheel and appurtenances to describe a horizontal 

 curve, to which the direction of its axis at the commencement of the 

 motion is a tangent, we shall perceive a strong tendency in the wheel 

 to leave the vertical and assume the horizontal position.* 



4. To illustrate the effect of removing atmospheric resistance and 

 obviating friction, I have constructed a delicate metallic wheel about 

 thr-ee inches in diameter, through the centre of which passes a steel 

 axis about one tenth of an inch in diameter and three inches long. 

 Near each end of this axis a hole is drilled to receive a delicate 

 thread of loosely twisted silk, by which the two ends are supported 

 and the axis kept in a perfectly horizontal position ; the other ends 

 of the silk threads are fastened to two hooks on the bottom of a cyl- 

 indrical mass of lead, which is in turn supported by a single hook in 

 the centre of its upper base. The wheel is made to revolve On its 



* This neat little experiment had been made, and was first coninuinicated to me 

 by Mr. William Masou, who, to render it the more striking, had mounted the wholse 

 box on a pointed axis passing longitudinally through the centre of gravity. 



