Famous Scientists 561 



due to the resistance of the intervening circuit when bringing 

 an electromagnet into use at a great distance. The successful 

 demonstration of this principle was a forerunner of the develop- 

 ment of the electric telegraph. 



Henry prepared a device, operated by a current sent through 

 a long line of insulated wire, for making signals at a distance by 

 electromagnetism, and made interesting inventions for other pur- 

 poses. One of his electromagnets made for Yale college sus- 

 tained a weight of over a ton. He also succeeded in producing 

 an electric spark by means of purely magnetic induction. To- 

 gether with Faraday he laid the foundation for the modern study 

 and development of electromagnetism and electrical induction. 



In 1832 Henry was elected professor of natural philosophy 

 at Princeton. In 1846 he was chosen first secretary of the 

 Smithsonian Institution at Washington, a position he held until 

 his death in 1878. In 1849 he was elected president of the 

 American Association for the Advancement of Science, and in 

 1868 president of the National Academy of Sciences. He re- 

 ceived many other honors. 



Joule. James Prescott Joule was born at Safford, England, 

 in 1818, the son of a brewer. He studied at home and was for 

 the most part self-educated, although he received for some time 

 three lessons a week from the distinguished chemist, John Dalton. 

 He became interested in physics and made original researches in 

 his home laboratory. 



At the age of nineteen Joule constructed an electromagnetic 

 engine. He emphasized the importance of accurate measure- 

 ments in scientific work. He formulated the laws of the heating 

 effects of electric currents in a conductor. Working with Lord 

 Kelvin, he made important discoveries regarding the heat proper- 

 ties of gases. His discoveries regarding the condensation of steam 

 increased the efficiency of the steam engine. 



His services to science were recognized in many ways. He 

 was awarded the Royal medal of the Royal Society in 1852 and 

 the Copley medal in 1860, and received degrees from several lead- 

 ing universities. He was elected to membership in all the princi- 

 pal scientific societies of the world and was chosen president of 



