The following month Sir William Herschel, a British civil servant based in India, wrote to "Nature" saying that he had been using fingerprints (as a form of bar code) to identify criminals since 1860. However, Herschel did not mention their potential for forensic use. Over the years, Faulds conducted a bitter controversy with Herschel over the use of fingerprints, demanding proof in 1894 that Herschel had ever used fingerprints officially, which Herschel duly provided, and then writing a series of books and pamphlets many years later containing variations of the argument that he had been cheated his due credit (see for complete facsimiles of these and other fundamental works on fingerprinting, and the Herschel/Faulds letters). These books were published from 1905 onward, long after fingerprinting had come into widespread use.