KEY AND INDEX 



a star, in point of time his observations prece- 

 ding Bessel's, although Bessel's were much more 

 numerous. These observations solved the prob- 

 lem of star distance. 



Henry, Joseph, iii, 239; vi, 175. Born at Al- 

 bany, N. Y., Dec. 17, 1797; died at Washington, 

 D.C., May 13, 1878. An American physicist, 

 and secretary of the Smithsonian Institution. 

 Noted for his experiments in electro-magnetism. 

 He constructed electro-magnets of greater power 

 than any hitherto known, and was the first to 

 adopt insulated or silk-covered wire for the mag- 

 netic coil. He invented a magnetic bell for sig- 

 naling, which is considered the first example of 

 a true magnetic telegraph. Foreign estimates 

 place him in the foremost rank of American 

 physicists of the Nineteenth Century. 



Heraclides, i, 196. A Greek physician, who 

 decried the study of anatomy, depending en- 

 tirely upon the use of drugs for curing diseases. 

 He is said to be the first physician to use opium 

 in painful affections. 



Hero, i, 242. Alexandrian mathematician of 

 the Third Century, B.C. He wrote several 

 works, only one of which, "Pneumatics," has 

 been preserved. In his studies of gas, liquids 

 and solids, he shows a fairly clear conception of 

 the "atomic" nature of matter. He describes 

 also the mechanism of various mechanical toys 

 and devices, among them a ball rotated by the 

 action of steam. 



Herodotus, i, 103. Born at Halicarnassus, 

 Asia Minor, about 484 B.C. ; died at Thurii, 

 Italy, about 424 B.C. Celebrated Greek histo- 

 rian, called "the Father of History." In his 



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