244 



Lightning-rods, 80. 



dangerous conductors, 81. 

 Loadstone, 20, 21. 



Maury, Lieut., deep-sea soundings, 155. 

 Magnes, Magnesia, 20. 

 Magnet, electro. See Electromagnet. 

 Magnetic earth poles, 23, 32. 

 Magnetic lines of force, 31, 34, 60. 

 Magnetic needle, 21. 



variation of, 22. 



dip of, 22. 



action of, 33. 

 Magnetism, history of, 20. 



and electricity mutually dependent, 24. 



theories of, 24. 



in iron and -ted. 25. 



in tin- <-art.il. 32, 36. 



and -nil spots, 37. 



Magnetization, limit of, 31. 



Marconi, wireless telegraphy, 178-180. 



Measurement of electricity, 83. 



ampere, unit of, 85. 



method of, 86. 



Mercury luminous by shaking, 7. 

 Micro farad, unit of capacity, 110. 

 Molecules of iron and steel natural magnets, 25. 



and atoms, 30. 



Morse, S. F. R, devises code of telegraphic sig- 

 nals, 95. 



induces Congress to construct line, 96. 



transmits battery current through water, 



177. 

 Motion universal, 38. 



causes sound, hoat. light, and electricity, 39. 

 Multiple transmission, Ch. XIII, 114. 



duplex, 116. 



quadruplex, 118. 



