The next step was to bring more energy into play, still using Leyden jars; and for this purpose Dr. Morton placed within the circuit between the jars a Tesla oscillating coil. He was thus able to use in his shadow pictures the most powerful sparks the machine was capable of producing (twelve inches), sending the Leyden-jar discharge through the primary of the coil, and employing for the excitation of the vacuum tube the "step up" current of the secondary coil with a potential incalculably increased. While Dr. Morton has in some of his experiments excited his Leyden jars from an induction coil, he thinks the best promise lies in the use of powerful Holtz machines; and he now uses no Leyden jars or converters, thus greatly adding to the simplicity of operations. In regard to the bulb, Dr. Morton has tested various kinds of vacuum tubes, the ordinary Crookes tubes, the Geissler tubes, and has obtained excellent results from the use of a special vacuum lamp adapted by himself to the purpose. One of his ingenious expedients was to turn to use an ordinary radiometer of large bulb, and, having fitted this with tin-foil electrodes, he found that he was able to get strongly marked shadow pictures. This application of the Röntgen principle will commend itself to many students who, being unable to provide themselves with the rare and expensive Crookes tubes, may buy a radiometer which will serve their purpose excellently in any laboratory supply store, the cost being only a few dollars, while the application of the tin foil electrodes is perfectly simple.