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Rh to the electricity which they develop when rubbed together, each substance being positively electrified when rubbed with any substance beneath it in the list.

1. Cat's skin. 2. Flannel. 3. Ivory. 4. Glass. 5. Silk. 6. Wood. 7. Shellac.

8. Resin. 9. Metals. 10. Sulphur. 11. Caoutchouc. 12. Gutta-percha. 13. Gun-cotton.

Thus, if resin be rubbed with cat's skin, or with flannel, the cat's skin or flannel will be positively, and the resin negatively, electrified; while if glass be rubbed with silk, the glass will be positively, and the silk negatively, electrified, and so on.

86. It is not our purpose here to describe at length the electrical machine, but we may state that it consists of two parts, one for generating electricity by means of the friction of a rubber against glass, and another consisting of a system of brass tubes, of considerable surface, supported on glass stems, for collecting and retaining the electricity so produced. This latter part of the machine is called its prime conductor.

87. Let us now suppose that we have set in action a machine of this kind, and accumulated a considerable