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 (§ 11 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, § 12. 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. 14. KNOCHENHAURER’S EXPERIMENTS. CONDUCTING POWER OF GAS. SPARK. PENETRATING POWER. RELATION OF E. M. F. TO PRESSURE OF GAS. 1834. _Pogg. Ann._, Vol. LVII., and _Gordon_, Vol. II. Boltzmann’s experiment (_Pogg. Ann._, CLV., ’75), and calculation indicated that a gas at ordinary pressure and temperature must have a specific resistance at least 10^{26} times that of copper. _Pogg. Ann._, CLV., ’75. Sir William Thomson (Kelvin) confirmed this limit for steam, and Maxwell the same for mercury and sodium vapor, steam and air. From _Maxwell’s MSS._ Herwig was not sure but that the Bunsen burner flame and mercury vapor conducted. He allowed for the conductivity of the walls of the glass container. Braun treated of the conductivity of flames. _Pogg. Ann._, ’75. 14_a_. Varley found that 323 Daniel cells only just initiated a current through a hydrogen Geissler tube, and only 308 cells continued the current after once started. Knochenhaurer found that Harris’ (_Phil. Trans._, 1834) law did not hold exactly true, and that the _ratio_ between the E. M. F. and the air pressure becomes _greater and greater_ as the pressure becomes less and less. Harris thought the ratio was constant. The limits of his pressures were from 3 to 27.04 inches of mercury. Stated in other words, his results were the same as those of Harris and Masson (_Ann. de Chimie_, XXX., 3rd Se.), except that a small constant quantity should be added. § 16.