there remains a continuing use of the method in the study of rare processes and in other branches of science, such as autoradiography in medicine and biology. For a comprehensive and technically detailed account of the subject refer to the books by Barkas and by Powell, Fowler and Perkins. For an extensive review of the history and wider scientific context of the nuclear emulsion method, refer to the book by Galison. History Following the 1896 discovery of radioactivity by Henri Becquerel using photographic emulsion, Ernest Rutherford, working first at McGill University in Canada, then at the University of Manchester in England, was one of the first physicists to use that method to study in detail the radiation emitted by radioactive materials. In 1905 he was using commercially available photographic plates to continue his research into the properties of the recently discovered alpha rays produced in the radioactive decay of some atomic nuclei. This involved analysing the darkening of photographic plates caused by irradiation with the alpha rays. This darkening was enabled by the interaction of the many charged alpha particles, making up the rays, with silver halide grains in the photographic emulsion that were made visible by photographic development. Rutherford encouraged his research colleague at Manchester, Kinoshita Suekiti, to investigate in more detail the photographic action of the alpha-particles. Kinoshita included in his objectives “to see whether a single 𝛂-particle produced a detectable photographic event”. His method was to expose the emulsion to radiation from a well measured radioactive source, for which the emission rate of 𝛂-particles was known. He used that knowledge and the relative proximity of the plate to the source, to compute the number of 𝛂-particles expected to traverse the plate. He compared that number with the number of developed halide grains he counted in the emulsion, taking careful account of 'background radiation' that produced additional 'non-alpha' grains in the exposure. He completed this research project in 1909, showing that it was possible “by preparing an emulsion film of very fine silver halide grains, and by using a microscope of high magnification, that the photographic method can be applied for counting 𝛂-particles with considerable accuracy”. This was the first time that the observation of individual charged particles by means of a photographic emulsion had been achieved. However, that was the detection of individual particle impacts, not the observation of a particle's extended trajectory. Soon after that, in