Series of 21 notebooks numbered 1, 1A, 2, 2A, 3, 3A, 4-18 in Heaviside's hand mainly consisting of mathematical equations and calculations with drafts and transcripts of papers submitted to the Philosophical Magazine and the Electrician. The notebooks are frequently used from both directions. Heaviside usually wrote only on the right side pages, using the left side pages for additional notes or comments, often written at a later date. The subjects covered range from problems with long distance signal tranmsission and the development of a non-distortional circuit, duplex telegraphy, the age of the earth including the development of equations for heat loss from a spherical body, measurement of resistance, eletromagnetic theory of light, the transmission of an electric charge along a wire, Maxwell's equations, vector operators for mathematical calculations. There are occasional comments referring to his disputes with Sir William Preece and Lord Kelvin, and occasional verses or comments about other topics.