An important component of a biography of any great scientist is that the biographer also have deep scientific knowledge. This holds true for Silvanus P. Thompson, a scientist of distinction who authored this biography of Lord Kelvin. Thompson was a Fellow of the Royal Society, President of the Physical Society, President of the Institution of Electrical Engineers, and President of the Illuminating Engineering Society--all within a six year span. He also held the office of presidentfor other scientific organizations. This biography was begun in 1906 and published in 1910. It was re-issued in 1976 by Chelsea Publishing. The work is considered the definitive biography of Lord Kelvin. It includes Kelvin's personal recollections and data. His death in 1907 affected the project byextending the scope of the original work. He left letters, diaries, and other documents that supplemented the existing information. These documents would allow Thompson to create a much more comprehensive account of Kelvin's career than was previously possible. From the Preface by Thompson: ``It has been the author's desire to let documents and letters speak as far as possible for themselves; and if he has not always been able to avoid letting his own views tinge these pages, he has at leastendeavoured to avoid attributing to others that which is only his own. Doubtless there are many of Lord Kelvin's former pupils who will find gaps in the presentation of his life and character, as must needs be when the author can himself claim no nearer association than that of disciple. But thedisciple of one who was himself conspicuously faithful in little things, must at least try to be faithful. The peculiar and affectionate admiration, amounting in some almost to worship, which characterizes those who had the high privilege of that more intimate association, spreads far beyond their circle to the disciple. Let it be hoped that the affectionate admiration which he too shares may not have warped his judgment.''