Scientific American Supplement, No. 441, June 14, 1884. by Various
page 93 of 155 (60%)
page 93 of 155 (60%)
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160 mm. wide, meshes 40 mm. in breadth were advantageous and favorable
as regards rigidity. A reticulated ribbon like this, 4 meters in length, was made and formed into a flat ring having an external diameter of 1.42 m. and an internal one of 1.10 m. The resistance of this ring was found to be W = 0.3485 (1/_k_), and that of a plate one meter square, W0 = 0.368 (1/_k_). As the conductivity of the earth is very variable, and as we cannot have an absolute guarantee that the ramming will be uniform, it seemed proper to make the measurements of the resistance by fixing the plate and the ring in succession to the lower surface of a small raft, in such a way that the contact with the water should correspond as well as possible to the suppositions made for the calculation. As a second ground conductor, a system of water pipes was used, and, after this, a lightning rod conductor, etc. Repeated and varied experiments gave, for the calculation of the values of the resistances, equations so concordant that the following results may be considered very approximate. The square plate had a resistance of 35.5 Siemens units, and the reticulated ring one of 32.5. From the first figure we deduce k = 1/91.12, that is to say, the specific conductivity of river-water is 1:91120000. Calculation, then, gives as the resistance of the earth in Siemens units: Calculated. Observed. Square plate. 33.5 33.5 Annular ring. 31.76 32.5 |
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