In the "prospectus book" among the series of famous note-books, all the references and data apply to gas. The book is numbered 184, falls into the period now dealt with, and runs along casually with items spread out over two or three years. All these notes refer specifically to "Electricity vs. Gas as General Illuminants," and cover an astounding range of inquiry and comment. One of the very first notes tells the whole story: "Object, Edison to effect exact imitation of all done by gas, so as to replace lighting by gas by lighting by electricity. To improve the illumination to such an extent as to meet all requirements of natural, artificial, and commercial conditions." A large programme, but fully executed! The notes, it will be understood, are all in Edison's handwriting. They go on to observe that "a general system of distribution is the only possible means of economical illumination," and they dismiss isolated-plant lighting as in mills and factories as of so little importance to the public--"we shall leave the consideration of this out of this book." The shrewd prophecy is made that gas will be manufactured less for lighting, as the result of electrical competition, and more and more for heating, etc., thus enlarging its market and increasing its income. Comment is made on kerosene and its cost, and all kinds of general statistics are jotted down as desirable. Data are to be obtained on lamp and dynamo efficiency, and "Another review of the whole thing as worked out upon pure science principles by Rowland, Young, Trowbridge; also Rowland on the possibilities and probabilities of cheaper production by better manufacture--higher incandescence without decrease of life of lamps." Notes are also made on meters and motors. "It doesn't matter if electricity is used for light or for power"; while small motors, it is observed, can be used night or day, and small steam-engines are inconvenient. Again the shrewd comment: "Generally poorest district for light, best for power, thus evening up whole city--the effect of this on investment."