The London, Edinburgh and Dublin philosophical magazine and journal of science . on a metal bar B which slid into a rectangular brassbox A, 18 cm. long, 6 cm. deep, and 2 cm. wide, with metalflanges at both ends fitting between the rectangular poles ofa large electromagnet. One end was closed by a ground glassplate C, and the other by a waxed brass plate E, in the centreof which was cut a rectangular opening 1 cm. long and 3 This opening was covered by a thin plate of metalsof silver, aluminium or iron, whose stopping power fora particles lay between 4 and 6 cm. of air. The zinc sulph
The London, Edinburgh and Dublin philosophical magazine and journal of science . on a metal bar B which slid into a rectangular brassbox A, 18 cm. long, 6 cm. deep, and 2 cm. wide, with metalflanges at both ends fitting between the rectangular poles ofa large electromagnet. One end was closed by a ground glassplate C, and the other by a waxed brass plate E, in the centreof which was cut a rectangular opening 1 cm. long and 3 This opening was covered by a thin plate of metalsof silver, aluminium or iron, whose stopping power fora particles lay between 4 and 6 cm. of air. The zinc sulphidescreen F was fixed opposite the opening and distant 1 or 2 the metal covering. By means of two stopcocks, the a. Particles with Light Atoms. 543 vessel was filled with the gas to be examined either byexhaustion or displacement. It is a great advantage to havethe zinc sulphide screen outside the apparatus, in order toavoid contamination due to volatilized active matter, andfor the easv introduction of absorbing material between theend plate and the screen. Fiff. r~ <s \Y - % ? \ X In practice, the source was introduced info the brassvessel at a convenient distance from the screen, and the airexhausted. The a. rays after traversing the end plate fell onthe screen, and the marked luminosity due to them was aguide in fixing the microscope M in the centre of the diameter of the field of view (2 mm.) was less than thewidth of the opening (3 mm.). Since the number of H atoms observed under ordinaryconditions is less than one in a hundred thousand of thenumber of a particles, H atoms, projected in the directionof the a particles, can only be detected when the a, rays arestopped by the absorbing screens. It was not found possibleto bring an intense source closer tiian 3 cm. from the screenon account of the luminosity excited in it by the <y rays andswift /3 rays, which prevented counting of weak strong magnetic field was necessary to ben
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectscience, bookyear1840
