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 



