135. PENETRATING POWER OF X-RAYS INCREASED BY REDUCTION OF TEMPERATURE. § 23 and 72_b_ at end. Among the hundreds of ideas that occured to Edison in connection with Roentgen ray tests was that concerning what might happen by cooling the discharge tube to a very low temperature. As before, he maintained the tube in connection with the air pump so as to be able to vary the vacuum. The reduction of temperature was obtained by means of ice water. Of course the bulb could not be placed in the water itself on account of trouble which would occur from electrolysis, therefore, the discharge tube was immersed in a vessel of oil, § 13, which in turn was surrounded by a freezing mixture. The vessel was a stout battery jar 14 inches high, eight inches in diameter with glass walls 5/10 of an inch thick. The oil employed was paraffine. The refrigerating jar was 12 inches high and 12 inches in diameter and the glass wall thereof, 3/8 inch thick. He tested the difference in the power of the rays by first noticing the thickness of steel that was not penetrated by the rays generated from the tube while in air. Crucible steel 1/16 of an inch thick did not transmit rays sufficiently to illuminate the sciascope, and yet with the use of oil and reduction of temperature, and after the rays had passed through two thicknesses of glass as well as through the oil and ice water, the sciascope was made luminous by rays after passing through a plate of steel of double the thickness, __i.e.__ 1/8 in. thick. See in this connection, Tesla’s experiment, § 135, where powerful rays were obtained by immersing the discharge tube in oil. Accounts of these two experiments were published simultaneously. Tesla attributed the idea of this use of oil to Prof. Trowbridge of Harvard University, who showed that a discharge tube immersed in oil is adapted to the generation of X-rays of increased penetrating power. See cut at p. 135. [Illustration: SCIAGRAPH OF RATTLESNAKE BY USE OF STOPS. § 107., p. 101. By Leeds and Stokes. ]