(p. 64). The machines of Ctesibius and Hero. See vol. I., p. 242 _seq._, for a full account of these mechanisms. (p. 65). Toricelli, the pupil of Galileo, and his discovery of atmospheric pressure. For a fuller account of his discovery and what came of it see vol. II., p. 120 _seq._ (p. 66). Boyle's experiments on atmospheric pressure. See vol. II., p. 204 _seq._ (p. 66). Mariotte and Von Guericke. See vol. II., p. 210 _seq._ (p. 71). Roman mills. A scholarly discussion of the subject of Roman mills, based on a comprehensive study of the references in classical literature, is given in Beckmann's _History of Inventions_, London, 1846. (p. 73). Recent advances in water wheels. As stated in the text, the quotation is from an article on _Motive Power Appliances_, by Mr. Edward H. Sanborn, in the _Twelfth Census Report_ of the United States. CHAPTER V CAPTIVE MOLECULES; THE STORY OF THE STEAM-ENGINE (p. 82). The experiments of Hero of Alexandria. For a full account of the experiments see vol. I., pp. 249, 250. (p. 84). The Marquis of Worcester's steam engine. The original account appeared, as stated, in the Marquis of Worcester's _Century of Inventions_, published in 1663. (p. 92). Newcomen's engine. As stated in the text, the account of Newcomen's engine is quoted from the report of the Department of Science and Arts of the South Kensington Museum, now officially known as the Victoria and Albert Museum. (pp. 107-109). James Watt. The characterization of Watt here given is taken from an article in an early edition of the Edinburgh Encyclopædia published about the year 1815. CHAPTER VI THE MASTER WORKER (p. 112). High-pressure steam. The work referred to is Leupold's _Theatrum Machinarum_, 1725. (p. 122). Rotary Engines. The quotation is from the report of the Victoria and Albert Museum above cited. (pp. 127, 128). Turbine engines. The quotation is from an anonymous article in the London _Times_, August 14, 1907. (pp. 129, 130). Turbine engines. The quotation is from an article on _Motive Power Appliances_ in the _Twelfth Census Report_ of the United States, vol. X., part IV., by Mr. Edward H. Sanborn. CHAPTER VII GAS AND OIL ENGINES (pp. 135, 136, 137). Gas engines. Quoted from the report of the Victoria and Albert Museum above cited. (pp. 141-144). Gas engines and steam engines in the United States. Quoted from the report of the Special Agents of the _Twelfth Census_ of the United States, 1902. (pp. 146, 147). The Svea heater. From an article by Mr. G. Emil Hesse in _The American Inventor_ for April 15, 1905. CHAPTER VIII THE SMALLEST WORKERS In connection with this chapter the reader will do well to review various earlier portions of the work outlining the general history of the growth of knowledge of electricity and magnetism. For example: