66o POPULAR SCIENCE MONTHLY. 



them, and can we see farther into the recesses of the human body? 

 In regard to the first question, we can say that, although we may 

 not be able to answer dogmatically that we know w^hat these rays 

 are, we have valuable hints in regard to their character, and our 

 knowledge of their manifestations and their relation to light waves 

 and magnetic waves has greatly increased during the four years 

 which have elapsed since their discovery. They are now believed 

 by the best authorities to be magnetic and electrical pulses, or 

 waves of extremely short length. In the spectrum of sunlight 

 formed by sending a beam through a prism of quartz the X-ray 

 pulses or waves are to be found, according to this hypothesis, be- 

 yond the violet color of this spectrum — far into the dark region 

 invisible to the eye, and only brought into view at present by the 

 aid of photography. In this invisible region reside many singular 

 manifestations of energy closely analogous to those of the X rays. 

 The ultra-violet rays invisible to the eye have the property of 

 refraction. They can be bent out of their course by prisms made 

 of quartz. The X rays, however, can not be directed from a 

 straight course. This is their greatest peculiarity, and many at- 

 tempts, both mathematical and experimental, have been made to 

 elucidate it. It is not a fatal objection to the X rays being classed 

 with light waves, for, under certain conditions, even light waves 

 can be made to lose the power of being bent aside. 



Leaving for the present a further discussion of the question 

 What are the X rays? let us examine what the actual condition 

 of the art of using the rays is. Many attempts have been made 

 to improve the Crooke's tube, in which the rays are produced, but, 

 like the hand telephone, its form has remained -substantially unal- 

 tered since the first flush of discovery. Its present form consists 

 of a bulb of thin glass, exhausted of air, containing a little concave 

 mirror of ahmiinum, and opposite to this, separated by a gap of 

 several inches, is an inclined sheet of thin platinum, called the 

 focus plane, or anticathode. The electrical discharge passes be- 

 tween this plane and the mirror, and the X rays are thrown ofl" 

 from the inclined sheet of platinum. They are not reflected in 

 the ordinary sense of the term, but the electric rays converge from 

 the mirror to a spot on the platinum which glows with a red heat, 

 and the X rays emanate from the heated spot as if it were their 

 source. Thousands of investigators have endeavored to improve the 

 form of tube, but, with several important minor appendages, it still 

 maintains the principal features of an aluminum concave mirror and 

 an inclined plane of platinum. Aluminum is found to be the best 

 metal for the mirror from which the raj'S are generated, largely 

 because its metallic particles are not torn off by the discharge, as 



