Purcell was the author of the innovative introductory text Electricity and Magnetism. The book, a Sputnik-era project funded by an NSF grant, was influential for its use of relativity in the presentation of the subject at this level. The 1965 edition, now freely available due to a condition of the federal grant, was originally published as a volume of the Berkeley Physics Course. Half a century later, the book is also in print as a commercial third edition, as Purcell and Morin. Purcell is also remembered by biologists for his famous lecture "Life at Low Reynolds Number", in which he explained a principle referred to as the Scallop theorem.