Length. Diameter. Vertical cylinder buried 1.40 m. 0.13 m. " " " 1.80 m. 0.06 m. Vertical bar " 2.60 m. 0.013 m. Horizontal bar " 5.20 m. 0.013 m.
Horizontal flat ring 1.32 m. in external diameter, and 1.08 m. internal.
Horizontal network 1.01 m. square, and having meshes of the same size as those of the reticulated ribbon.
Horizontal reticulated ribbon 3 m. in length and of the structure described.
Horizontal annular ring 1.26 m. in external diameter, 0.94 m. internal.
In conclusion, let us meet an objection that might be made to the accuracy of the hypotheses that serve as a base to the preceding calculations, in cases where ground plates for lightning rods and not for telegraphs are concerned. Between the two ground plates of a telegraph line there is generally a distance such that the curves of the current undergo no deviation in the vicinity of one of the electrodes (the only part important for integrations) through the influence of the other. But it might be admitted that such would prove the case with a lightning rod in a storm, at the time of the passage of the fluid into the earth. The ground plate here is one of the electrodes, and the other is replaced by the surface of the earth strongly charged to a great distance under the storm clouds. If we suppose (what may be admitted in a good lightning rod) that there no longer occurs any spark from the point downward, the curves of the current, in starting perpendicularly from the ground plate, would be obliged to leave their rectilinear trajectory and strike the surface of the earth at right angles. When the electricity flows through a plane surface into an infinite body, it is only when such surface presents a very great development that the respective potentials decrease very slowly in the vicinity of the said surface. No notable modification occurs, then, in the curves of equal potential, in the vicinity of the ground plate through the action of this extended charge, nor consequently any modification in the curves of the current; but the electricity which spreads has but a short distance to travel in order to overcome the most important resistances.
The calculations of resistances given above have, then, the same value for discharges of atmospheric electricity.—Bull. du Musee de l’Industrie.
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By H. SCHUCHT.
Concerning the separations which take place at the positive pole, the composition of the peroxides, and the manner of their determination, relatively little has been done.