APPENDIX 



Mr. Hewitt's mercury-vapor tube, the chapter on "Newton and 

 the Composition of Light" (vol. II., p. 225 seq.} may be consulted. 

 Also "Modern Theories of Heat and Light," vol. III., p. 206 seq. 



CHAPTER XII 



THE MINERAL DEPTHS 



The chapter on "The Origin and Development of Modern 

 Geology," vol. III., p. 116 seq., may be read in connection with 

 the allied subjects here treated. 



In preparing the section on the use of electricity in mining, the 

 article by Thomas Commerford Martin, entitled Electricity in 

 Mining, in the United States Census Report of 1905, has been 

 freely drawn upon. The quotations on pp. 262, 266, 268, and 

 270 are from that source. 



CHAPTER XIII 



THE AGE OF STEEL 



See note under chapter XII. 



CHAPTER XIV 



SOME RECENT TRIUMPHS OF APPLIED SCIENCE 



In connection with various portions of this chapter the reader 

 will find much that is of interest in the story of chemical develop- 

 ment in general as detailed in volume III., pp. 3-72 inclusive. 



Also various chapters on electricity as outlined under chapter 

 VII. above. 



(p. 310). Nitrogen from the air. The quotation is from the 

 Engineering Supplement of the London Times, January 22, 1908. 



[325] 



