This electrical process of evacuating varies in its rapidity according to the thinness of the glass. Here again he noted the application of his theory in that an easier passage was afforded for the ions. § 47. A few minutes of operation produced through thin glass, a vacuum from very low to very high, whereas, to obtain the same vacuum through much thicker glass over 1/2 hour was necessary. Again with a thick electrode the time required was much greater. The small hole was not always visible and it was thought that the material went through the pores. The result obtained by the following experiment tends to uphold Mr. Tesla’s emission theory. 139_a_. LAFAY’S EXPERIMENT. GIVING TO X-RAYS THE PROPERTY OF BEING DEFLECTED BY A MAGNET BY PASSING THEM THROUGH A CHARGED SILVER LEAF. _Comptes Rendus_, March 23, ’96 and April 7, 13, 27, and _L’Ind. Elec._, April and May ’96. From trans. by Louis M. Pignolet. He placed at about .5 cm. below a discharge tube, a lead screen pierced by a slit 2 mm. wide; and 0.04 m. lower, a second lead screen having a slit 5 mm. wide completely covered by an extremely thin leaf of silver. Opposite the silver leaf and exactly in the axis of the slit, was fixed a platinum wire 1.5 mm. diameter. Thus, the rays which passed successively through the two slits projected a shadow of the wire on a photographic plate below. When the silver leaf was connected to the negative pole of the induction coil that excited the tube, the rays, which had become electrified (§ 61_b_, p. 47) bypassing through the leaf, were deflected by a magnetic field of about 400 L. G. S. units, whose lines of force were parallel to the slit. The direction of the deflection was determined by the same law as that of the deflection by a magnetic field of the cathode rays in the interior of a discharge tube. § 59. When the silver leaf was not connected to the coil, no deflection was produced. § 79. To double the apparent deflection, one part of the slit was covered by a lead plate during the first half of the experiment. The lead plate was removed and placed over the other part of the slit, and the direction of the magnetic field reversed during the last half of the experiment. Thus the distance on the sciagraph between the two parts of the wire, was double the deflection produced by the magnetic field.