CHARLES B. WARRING. 171 
anywhere near the horizontal there is only the excess of 
influence of one of the gyroscopes over the other, but 
when it hangs down nearly vertical, it has no resisting 
power, and produces only the effect of so much weight 
hung on the other. I now set both in motion, the wheels 
rotating in opposite directions, the lower one drops down 
as you see, and the whole rotates somewhat rapidly 
around the shaft. I now stop the rotation of the lower 
wheel, the system revolves almost exactly as before. 
It may possibly be thought that the statement in the 
~ Montreal address as to the direction of the wheels was a 
slip of the pen. But under it all and woven into it, is 
the belief that the peculiar sustaining power of a gyro- 
scope is independent of the horizontal movement. It is 
impossible for one who thinks so, to have a knowledge 
of the ‘‘ true inwardness”’ of gyrating bodies. For all 
sustaining power is absolutely gone the moment the 
horizontal movement ceases, and conversely the mo- 
ment the nutation ceases, the precessional movement 
ends. By nutation I mean, of course, the falling or 
rising of the free end of the instrument, and by the pre- 
cession, I mean the lateral movement. 
As these statements are of great importance, I shall 
now prove their truth by experiment. 
And, first, that the sustaining power ceases when the 
horizontal movement ceases, or, to use Sir William Thom- 
son’s words, when there is ‘‘no moment of momentum.”’ 
I set my instrument in motion. At one end is a pin 
projecting a short distance. I attach to a fixed standard 
a string which when horizontal is at the same height from 
the table as the gyroscope. As the instrument swings 
around, I catch the string on the pin. The instant it is 
. drawn taut, the wheel drops. The so called gyroscopic 
power sustaining it, is gone. 
In each of these, and in the previous experiments, the 
string was at right angles to the motion, and, conse- 
Wai eisl, 
