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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1919 Excerpt: ...windows at each end, and glass windows at the sides. A fine rod stands erect within, carrying a piece of glass fibre rendered electrically conducting (or, of course, a gold leaf). This stem is supported by a plug of sulphur, and projects downwards a little, so that the piston (2) can be moved up by rotating the cam (3), and thus connect the leaf stem with batteries. On lowering the stem this connection is broken, the brass guard tube, however, remaining charged. It is seen that no electricity can leak away from the stem except by ionisation taking place within the instrument, owing to radiation entering by the lead windows. There will, of course, be a natural leak (N-), due to slight radioactivity of the air and inner surface of the lead. But if old lead be used, this leak may be reduced to a very small value. The cam is operated by twisting the rod (4) between two stops. The movement of the leaf is read by a microscope. Great care should be taken to see that the air of the room is still when the electroscope is used, or otherwise differences of temperature upon different sides of the instrument will set up air currents within, which vitiate the results. And it is essential to leave the leaf charged for a few hours before making a test. Owing to the curious tendency of insulators to soak up electric charges, time must be allowed for the sulphur to become saturated before beginning work. The lead barrel being connected to earth, readings are taken when each of the two quantities of radium to be compared stand at some definite distance from one of the lead windows, and a comparison of these results, if one of the radium tubes has been standardised against a known quantity of pure radium salt, will enable the quantity in the other tube to be determined. It wou...
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