The penetrating power of the rays emitted permits the production of skiagraphs; the plates were enveloped in Carbutt’s black paper (impermeable to light), and on them were laid pieces of tinfoil cut in openwork pattern; after one hour’s exposure negatives were secured plainly showing the pattern. Analogous experiments were carried on with the specimens from Paris, but they were only one fifth as strong in effects; that labelled ‘polonium sub-nitrate’ had positively no action on the plates used. The primary source of the energy manifested by these extraordinary substances has greatly puzzled physicists, and as yet remains a mystery. Mme. Curie, speculating on the matter, conjectured that all space is continually traversed by rays analogous to Röntgen rays, but far more penetrating, and not capable of being absorbed by certain elements of high atomic weight, such as uranium and thorium. Becquerel, reflecting on the marvellous spontaneous emission of light, said: “If it can be proved that the luminosity causes no loss of energy, the state of the uranium is like that of a magnet which has been produced by an expenditure of energy and retains it indefinitely, maintaining around it a field in which transformation of energy can be effected; but the photographic reductions and the excitation of phosphorescence require an expenditure of energy, of which the source can only be in the radio-active substances.” Somewhat later, Becquerel hazarded the opinion that the radiation is composed at least in part of cathodic rays; but these have been proved to be material, hence the induced activity must be caused by material particles impinging upon the substances excited. This materialistic theory seems to be confirmed by the results of ingenious experiments made by Mme. and M. Curie; they placed a sensitive plate beneath a salt of radium supported on a slab of lead, in the vicinity of an electro-magnet. Under these conditions, when the current was passing, the rays emitted were bent in curved lines upon the sensitive plate, making impressions. It may be objected, says a French writer, that the materialistic theory requires us to admit actual loss of particles of matter, nevertheless the charges are so feeble that the most intense radiation yet observed would require millions of years for the removal of one milligram of substance. While writing these lines, we have news of experiments that seem to throw doubt on the elementary character of these radio-active bodies; Bela von Lengyel, of Budapest, claims to have prepared the so-called ‘radium’ synthetically. By fusing with the heat of electricity uranium nitrate mixed with a small percentage of barium nitrate, and treating the mass with acids, he obtained a substance that gives out actinic rays, Röntgen rays, excites platino-cyanid screens and causes air to conduct electricity; in short, the Hungarian chemist gets material possessing all the properties characteristic of the ‘element’ announced by Mme. Curie.