488 



INDEX 



Wright of Durham, author of the 

 Grindstone Theory, 386 



XERXES, entertained at Abdera, 131 

 Ximenes, Cardinal, destroys valu- 

 able manuscripts, 154 



YEAR, early measures of, 53 

 Young, Dr. Thomas, on interfer- 

 ence, 346 



Young, Prof. C. A., on strength of 

 gravitation, 445 



ZENOPHANES, early ideas of geology, 



148 



Zero, introduction of, 58 

 Zodiac, circle of the animals, 104 

 Zone of no shadow around Syene, 



59 

 Zones, first conceptions of, 101 



THE END 



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