USEFUL AETS. 



CHAPTER XVII. 

 OSCILLATION. UNITED STRENGTH. THE DOME. 



Connection of Oscillation with Centrifugal Force. Equality of Time in Oscil- 

 lation. The Spider. The Stone and String. Pendulum of the Clock, and 

 its Effect on the Machinery. Acceleration and Retardation. Compensating 

 Pendulums. The Metronome, and its Use in Music. A simple Metronome. 

 Value of the Instrument in War. The Escapement, and its Connection 

 with the Pendulum. Mode of Action. Larva of Burying-beetle. Earth- 

 worms and Serpents. Union is Strength. The Hippopotamus Rope and its 

 Structure. The Spider-web. Distinction between the Threads. Principle 

 of the Dome. The Arch, and its Connection with the Dome. Esquimau! 

 Huts. Receiver of the Air-pump, and its Power of Resistance. The Human 

 Skull and the Egg. Accidental Resemblance. The Salad-dressing Bottle. 

 The Medusa, Strobila, and Hydra. 



A PORTION of our last chapter dealt of Centrifugal Force. 

 "We will now proceed to another well-known power, 

 which seems to be a variation, or perhaps a division, of the 

 same power. I mean the principle of OSCILLATION, which has 

 done so much for the present state of the world. I mention 

 the connection of the two principles because it is evident that, 

 if Oscillation were continued in one direction, it would be 

 converted into centrifugal force. In fact, it can only be 

 considered as centrifugal force interrupted. 



The chief point in this subject is the equal time occupied 

 by the oscillating body, no matter what may be the " arc " 

 distance through which it sways, provided that the length of 

 the line remains the same. The discovery of this principle by 

 Galileo in a church at Florence is too well known to need 

 repetition. 



This principle may be observed by any one, and at almost 

 any time. The Spider at the end of its line illustrates it, and 



