Electricity for public schools and colleges . allel discharges upon one another. Dr. Crookes has recently verified experimentally that two paralleldischarges in a low vacuum obey Amperes laws of parallel currentsgiven in Chapter XVIII. § i6. § 15. Discharge in High Vacua. The remarks made in (a) and (?) of § 14 apply also to the presentsection. We now proceed to mention briefly the phenomena peculiarto high vacua. To Dr. Crookes is due our knowledge of these inter-esting and beautiful phenomena. (a) Let us suppose that the tube in the figure has a negative poleat the centre, and a positive pol
Electricity for public schools and colleges . allel discharges upon one another. Dr. Crookes has recently verified experimentally that two paralleldischarges in a low vacuum obey Amperes laws of parallel currentsgiven in Chapter XVIII. § i6. § 15. Discharge in High Vacua. The remarks made in (a) and (?) of § 14 apply also to the presentsection. We now proceed to mention briefly the phenomena peculiarto high vacua. To Dr. Crookes is due our knowledge of these inter-esting and beautiful phenomena. (a) Let us suppose that the tube in the figure has a negative poleat the centre, and a positive pole at each end. 3So ELECTRICITY CH. XXII. When the exhaustion is what is usually called good for a lowvacuum, say, for example, that the pressure is only half a millimetreof mercury or about yr^^,^ of an atmosphere, there is observed on eachside of the negative electrode a dark space, this space being boundedby a brilliant luminosity. Many experiments tend to show that theextent of this dark space measures the mean free path of those mole-. FiG. i. cules which are charged by contact with the — pole and are thenrepelled. It seems that such molecules are projected from the —pole normally to its surface ; they beat back the other molecules, andat the surface over which this conflict is most energetic there is thebrilliant light as evidence of the energy. There is no dark space atthe positive pole. (/3) As the exhaustion proceeds, the dark space (or mean free pathof the molecules) increases, and at last the dark space extends rightacross the vessel, and the molecules projected normally from the —pole bombard the glass on the opposite side. It appears that allordinary glass thus bombarded exhibits a peculiar greenish phosphor-escence. Many precious stones and minerals are rendered beautifullyluminous by this molecular bombardment. This projection takesplace from the — pole only, and it proceeds straight from it, no matterwhere the + pole may be. In the figure we see to the
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Keywords: ., bookcentury1800, bookdecade1890, bookpubl, booksubjectelectricity
