INDEX 315 



Weighing, 63 Work, definition, 58 



Weight, 51, 61, 63 Wrought iron, 152 

 measurement of, 51, 52 * 



Wells, 85, 86 * Yolk of an egg, 299 



Wheel and axle, 59, 60 



Winds, 112 Zenith, 20 



constant, 112 Zinc, 155 



trade, 113 Zones of light, 25 



