CHAPTER XIV. VOLTAIC ELECTRICITY 193 CHAPTER XV. MAGNETISM AND ELECTRO-MAGNETISM 206 CHAPTER XVI. ELECTRO-MAGNETIC MACHINES 211 CHAPTER XVII. THE ELECTRIC TELEGRAPH 218 CHAPTER XVIII. RUHMKORFF'S, HEARDER'S, AND BENTLEY'S COIL APPARARATUS 230 CHAPTER XIX. MAGNETO-ELECTRICITY 241 CHAPTER XX. DIA-MAGNETISM 247 CHAPTER XXI. LIGHT, OPTICS, AND OPTICAL INSTRUMENTS 255 CHAPTER XXII. THE REFRACTION OF LIGHT 298 CHAPTER XXIII. REFRACTING OPTICAL INSTRUMENTS 303 CHAPTER XXIV. THE ABSORPTION OF LIGHT 327 CHAPTER XXV. THE INFLECTION OR DIFFRACTION OF LIGHT 328 CHAPTER XXVI. THE POLARIZATION OF LIGHT 335 CHAPTER XXVII. HEAT 352 CHAPTER XXVIII. THE STEAM-ENGINE 406 CHAPTER XXIX. THE STEAM-ENGINE--_continued_ 418 [Page 1] INTRODUCTION. Although "The South Kensington Museum" now takes the lead, and surpasses all former scientific institutions by its vastly superior collection of models and works of art, there will be doubtless many thousand young people who may remember (it is hoped) with some pleasure the numerous popular lectures, illustrated with an abundance of interesting and brilliant experiments, which have been delivered within the walls of the Royal Polytechnic Institution during the last twenty years. On many occasions the author has received from his young friends letters, containing all sorts of inquiries respecting the mode of performing experiments, and it has frequently occurred that even some years after a lecture had been discontinued, the youth, now become the young man, and anxious to impart knowledge to some "home circle" or country scientific institution, would write a special letter referring to a particular experiment, and wish to know how it was performed. The following illustrated pages must be regarded as a series of philosophical experiments detailed in such a manner that any young person may perform them with the greatest facility. The author has endeavoured to arrange the manipulations in a methodical, simple, and popular form, and will indeed be rewarded if these experiments should arouse dormant talent in any of the rising generation, and lead them on gradually from the easy reading of the present "Boy's Book," to the study of the complete and perfect philosophical works of Leopold Gmelin, Faraday, Brande, Graham, Turner, and Fownes.