128_a_. GEORGES MESLINS INSURED A REDUCTION OF TIME FOR TAKING SCIAGRAPHS BY THE DEFLECTION OF THE CATHODE RAYS BY MEANS OF A MAGNETIC FIELD. _Comptes Rendus_, March 23 and 30, 1896. From trans. by Louis M. Pignolet. The method consists in using a permanent or electro-magnet to create a magnetic field perpendicular to the cathode rays in the tube. By this means, the active fluorescent spot on the tube is condensed, and the intensity of the X-rays generated there is increased. Another advantage is that, when the active part of the tube becomes inactive owing to the formation of a light brown deposit upon it, another part can be used by very slightly altering the position of the magnets. Thus, each time a new part of the tube can be used. The magnetic field must not be uniform but must have a suitable variation to produce the desired concentration of the cathode rays. A. IMBERT AND H. BERTIN-SANS’ EXPERIMENT. (_Comptes Rendus_, March 23, ’96. (From trans. by L. M. P.) They shortened the time by use of a magnet. JAMES CHAPPIN’S EXPERIMENT. (_Comptes Rendus_, Mar. 30,’96. (From trans. by L. M. P.)—Claimed priority in having shown publicly, on Feb. 19, a sciagraph of a hand, marked “Photograph obtained by concentration of the cathode rays, by means of a magnetic field.” The increase of the intensity of the X-rays obtained by this means was in the proportion of 8 to 5, as measured by the time of fall of the leaves of a Hurmuzescu electroscope. Prof. Trowbridge, of Harvard University, in a lecture, gave an interesting review (_Western Elect._, Feb. 29, ’96) of the length of time required in the early days of photography. Improvements are being made whereby the duration required in sciagraphy becomes less and less. In 1827, by heliography, 6 hours’ exposure was necessary; in 1839, by daguerreotype, 30 minutes; in 1841, by calotype, 3 minutes; in 1851, by collodion, 10 seconds; in 1864, by collodion, 5 seconds; in 1878, by gelatine, 1 second. The author remembers the photographs for use in the Edison kinetoscope were taken at the rate of 20 per second. The focus tube brings the time of exposure in behalf of X-rays down to a matter of seconds instead of minutes. For an admirable review of authorities, facts and theories relating to the causes of the darkening of photographic plates by light, see Cottier, in _Elect. World_, N.Y., May 23, ’96. 129. SIZE OF DISCHARGE TUBE TO EMPLOY FOR GIVEN APPARATUS.—A small tube required but a small E. M. F., and therefore should be employed with a small induction coil. The greater the distance of the sensitive plate and the object, considered together, from the discharge tube, the sharper the shadow. In short exposures, the tube should be small and at a short distance.