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12. Lullin’s Experiment. Spark. Penetrating Power. Passage Through Solids. Encyclo. Brit. Article Electricity. He placed a piece of cardboard between two electrodes and discovered that a spark penetrated the material and left a hole with burnt edges. When the electrodes were not exactly opposite each other, the perforation occurred in the neighborhood of the negative pole. Later experiments have shown that a glass plate, 5 or 6 cm. in thickness, can be punctured by the spark of a large induction coil. The plate should be large enough to prevent the spark from going around the edges. The spark is inclined, also, to spread over the surface of the glass instead of piercing it, ssss1. Glass has been cracked by the spark in some experiments.

13. Fage’s Experiment. Spark. Penetrating Glass. Holes Close Together. Practical Application. La Nature, 1879. Nature, Dec. 26, 1879, p. 189. The length of the spark from the secondary coil in air was 12 cm. One terminal of the secondary passed through an ebonite plate (18 cm. × 12) and touched the glass. Olive oil was spread around said terminal (ssss1 at end), and served to insulate the same. Oil dielectric in this connection originally employed at least prior to 1870. Remembered by Prof. Anthony as far back as 1872, who often performed the experiment according to instructions contained in a publication. The other terminal of the secondary coil was brought against the glass opposite the first terminal. The spark was then passed and the glass perforated, ssss1. By pushing the glass along to successive positions and passing the spark at each movement, holes could be made very close together. In Nature, of 1896, the author noticed that certain manufacturers were introducing glass perforated with invisible holes to be used for windows as a means of ventilation without strong draughts. Perhaps the fine holes were made by means of the electric spark.