i44 POPULAR SCIENCE MONTHLY
their course by passing at an angle from one transparent body to another. This property, known as refraction, is the cause of the formation of images by convex transparent bodies or lenses. But, strangely, the rays of light above mentioned do not act like ordinary light. All objects are transparent to them, though not in equal degree. Not being stopped by dense bodies they are not refracted. Not being affected by lenses they do not produce vision in the eye. As we can not see them to the eye they are not light. But their effect on chemical decomposition is the same as that of light. Hence while not available for vision they can be used in photography. But not being refracted they produce no definite image on the sensitive plate. But they may give rise to shadows. They do not pass through all opaque objects with equal readiness. Hence to place an opaque body between the rays and a sensitized plate would be to cast some kind of a shadow on that plate. The shadow means an arrest of the chemical changes which are the basis of photography. Then if the opaque body be not in all parts of equal density the shadow becomes deeper in some places than in others. This gives on the photographic plate some idea of the intimate nature of the object photographed. For the density is not merely a matter of the surface of bodies. It pertains to the interior, which in an opaque object can not be seen, but which nevertheless may be photo- graphed in this fashion by these peculiar rays.
This line of investigation was lately developed in experiment by Professor Eontgen, and the strange character of the i X-rays ' or ' cathode rays ' is now a matter known to every one. By means of these non-refracting rays, shadow photographs can be made showing the bones of the skeleton, imbedded bullets, the contents of a pocket-book, or any similar hidden object which has a nature or a density unlike that of its containing surface. These experiments of Eontgen have been varied and verified in every conceivable way. A wonderful mythology is growing up around them, to the confusion of those who have not paid attention to the series of experiments which made Eontgen's discoveries simple and inevitable.
" For example, in a thousand places the Eontgen rays and the bacilli of disease are made to work together to fill the purse of the enterprising physician. The doctor examines the internal organs of the patient with the fluorescent tubes. He finds out how and where the germs of disease are working their devastation. Then he turns the mysterious X-rays upon these germs and they are checked in their career of ruin : shrivelled up, it may be, under this marvelous light, as caterpillars shrivel on a hot shovel. Another physician I know of distributes his remedies by electric wire, one end in the bottle and the other in the mouth of the patient, miles away. Still other physicians, wise in their generation, use the X-rays and the microbes and the elec- tric currents with other mysterious agencies equally for their own profit