Propulsive Effects of a Rotating Mass 



However, this device does not function in either water or air, nor when 

 suspended from a thread, nor even on small blocks of dry ice that are free to 

 move on a horizontal slate. When the device is placed on a model of a ship, 

 for example, it makes the model go forward and backward, while the center of 

 gravity of the model remains in the same position. The device, therefore, func- 

 tions only if a suitable value of friction resistance exists; if this resistance is 

 too low or nonexistent, the device does not function. 



In order to give an explanation of this, it is necessary to consider only the 

 derivative of the quantity of motion (Fig. 8). Since the area of this diagram is 

 zero, it follows that, if there is no friction, the device goes back and forth; if 

 there is friction, linear or not, the device acquires a forward motion. 



In fact, if the friction resistance is represented by lines +Ra and -Rg as 

 indicated in Fig. 8, then the device advances and does not go back. This is so 

 because the diagram of force that thrusts the device back is always inferior to 

 the friction resistance, while in the meantime the point of the diagram of force 

 that thrusts the device forward is superior to the friction resistance. The de- 

 vice, in correspondence to this point, undergoes a forward jerk. If instead 

 the friction resistance is very low, the two lines +Ra and -Rg that represent 

 it come very close to the t axis, so that the two areas of the diagram remain 

 substantially equal between them, and the device does not advance. The device 

 thus remains defined, in both its functioning and its limited practical 

 applications. 



This conclusion cannot be extended to the devices indicated in Figs. 2 and 3. 

 They, in fact, function even with a very low friction, as can be seen in the tests 

 in water and on dry ice. On the other hand, if we analyze the trajectory of the 

 forward motion of the device (Fig. 27) deduced from Fig. 24, it is clearly indi- 

 cated that when the mass reaches point Pj and remains there motionless, the 

 device is displaced of +s^; when the mass is 

 in the remaining points of the trajectory, the 

 device goes forward and backward; when the 

 mass returns to Pi there is the h-Sj dis- 

 placement again; and thus it goes on. The 

 trajectory of the motion of the device is 

 therefore composed of two parts: one closed, 

 in which the device completes a back-and- 



forth motion, and the other open, giving proof Pi„ 27 - Trajectory 



of theforward motion of the device. It seems of devices (Figs, z and 



very difficult to give an explanation for this 3) that function with 



forward motion. On the one hand, we have very low friction 



definite proof that the device advances, even 

 in the presence of an extremely small amount 



of friction; on the other, we have the theorem of the motion of the center of 

 gravity, which excludes the possibility of the device advancing, unless there is 

 a friction resistance. No "internal" muscular force and no "internal" mecha- 

 nism, simple or complex, can influence the motion of the center of gravity. 



The explanation of the forward movement will eventually be found. What is 

 necessary is a thorough examination of the functioning of the device, both from 



1393 



