nothing, so that the said third electrode connected to the electrometer became slightly positive at all points within the hydrogen. § 4. The next step consisted in using a bulb, having oxydized copper electrodes and a hydrogen atmosphere at the pressure where there was only positive electricity, that is about 1/3 of an atmosphere. This remarkable phenomenon occurred; there was no positive electricity, but only negative. When the copper oxide was reduced, the positive electricity only, existed in all parts of the bulb. In brief, bright copper electrodes left a positive charge in the gas, while oxydized electrodes left a negative charge. He argued upon the results of this experiment to account for the delay in the passage of the electricity from the gas to the metal, § 46. In later experiments, he used the spectroscope to detect decomposition. § 6, at end. 48. DE LA RUE AND MÜLLER’S EXPERIMENT. HEAT STRIAE. _Phil. Trans._, vol. 159, 1878—They arranged for the best conditions, that is, when a small number of striae occurred in conjunction with a wide, dark interval. § 44. They found that the heat was greatest at the position of maximum luminosity, but they also found that heat was generated at the dark spaces. A novel feature was the discovery of the development of heat in the middle of the tube even when there was no luminosity, § 9_a_, near end, so that they thought it probable there may be what might be termed heat striae, independently of luminous striae. 49. SPOTTISWOODE AND MOULTON’S EXPERIMENT. SENSITIVE STATE. AIR-GAP IN CIRCUIT FORMS BEST METHOD OF OBTAINING. BRANCH CURRENT TO EARTH VERIFIED BY A TELEPHONE. SENSITIVE STATE BY A SINGLE QUICK DISCHARGE. _Phil. Trans._, 1879, p. 165, and April 8, 1880.—By sensitive state of luminous effects in a Geissler tube is meant the susceptibility of the light (§ 28) to an outside conductor connected to earth. Fig. 5, p. 17. When one’s hand is brought near a Geissler tube the change near the hand sometimes occurs and sometimes it does not. § 8. In the first place, the effect is more easily noticeable if the vacuum tube is comparatively wide or thick in diameter. With the electric egg, for example, the luminous effect, instead of extending more or less across the space between the electrodes, reaches from one of the poles to a conductor on the outside of the egg, provided said conductor has an earth connection or large capacity. Some of the light continues to exist nevertheless between the two poles. The general principle is that the division exists because of the re-distribution or branching of the disruptive discharge. It was not known why the luminosity should be affected by such an outside conductor sometimes, and remain the same at other times but the above named experimenters discovered causes which could be depended upon to produce the sensitive state. The apparatus will be described. They had the usual Geissler tube with the platinum wire electrodes, and a Holtz machine as the generator.