The small interrupter was found the more reliable, and seemed to shorten the needed time of exposure. A rotary contact-maker, giving two interruptions of the current per revolution, was also tested. This was driven by a motor with a condenser capacity of fourteen microfarads connected across the brushes. Owing to the large capacity of the condenser, a heavy current could be broken without marked sparking. The circuit breaker was tested at speeds ranging from 500 to 4,000 per minute, to note the influence on the time of exposure. The best results were obtained at the lower speed.... As no especial advantage could be noted when using the mercury breaker, it was abandoned for the vibrating interrupter.” This point is noted in detail, since so many experimenters seem to prefer such cumbersome devices, but they are, in reality, unnecessary. [Illustration: STINE’S EXPERIMENT, FIG. A. § 110. ] 110. APPARENT DIFFRACTION OF X-RAYS REALLY DUE TO PENUMBRAL SHADOWS. _Elec. Eng._, Apr. 22, ’96, p. 408.—By referring to the diagram marked “Stine’s Experiment, Fig. A,” the arrangement of the elements may be seen, while the photographic print is shown in “Stine’s Experiment, Fig. B.” p. 106. Prof. Stine described the investigation as follows: Diffraction is naturally one of the first kinematical points to be investigated in the Roentgen experiments. It was noticed that when the opaque object was some distance from the plate, pronounced penumbral shadows resulted. These were of such width as to indicate diffraction. However, when such shadows are plotted back to the tube they are found to be purely penumbral, and not caused by diffraction. To completely demonstrate this point the experiment illustrated in Fig. A was undertaken. Here A_{1} to A_{4} are brass plates one inch wide and 1/8 inch thick, and of the length of the dry plate employed. They were first fastened together, so as to leave two parallel slots 1/8 of an inch wide. These plates are placed within 3/8 of an inch of the bulb, were one inch apart, and rested 1-1/8 inches above the dry plate. The resulting sciagraph is shown in Fig. B. In the diagram S_{1} S_{2}, the edges of the penumbral shadow are very sharp and distinct. The direction of the rays is indicated, showing that there was absolutely no diffraction. This experiment has been modified in a variety of tests, with always the same result.” 110_a_. JEAN PERRIN’S NON-DIFFRACTION. _Comptes Rendus_, Jan. 27, ’96. From trans. by Louis M. Pignolet.—The active part of a tube was placed before a very narrow slit; 5 cm. further, there was a slit 1 mm. wide; 10 cm. further, there was the photographic plate. An exposure of nine hours gave an image with sharply defined borders, upon which there was no diffraction fringe. [Illustration: STINE’S EXPERIMENT. FIG. B. § 110. ] 159a. NON-REFRACTION.—Refraction was attempted with prisms of paraffine and of wax, but no refraction was noticed.