A YEAR OF THE X RAYS. 655 



tial high enough to give a spark of seA'^eral inches in air, and a 

 vacuum tube in which the spark was to be discharged, seemed to 

 be requisites, and wherever these were obtainable the experi- 

 ments were attempted. ' Poor facilities led to efforts to dispense 

 with good ones, the prevailing meagerness of equipment becom- 

 ing thereby a means all the earlier of deciding the limitations for 

 successful operation. Of course, the excitemeut quieted when the 

 novelty wore off, but investigations in this new field must con- 

 tinue for a long time. 



The pure physics of the subject was, naturally, the side which 

 most appealed to scientific professors. How was the strange 

 agent to be set to work, and how did it work ? Was it light, or 

 was it electricity ? Was it material, or ethereal ? Was it due to 

 the cathode or to the anode terminal of the vacuum tube ? The 

 year's work upon these questions leaves them answered only par- 

 tially and unsatisfactorily. Very little indeed has been added 

 to the facts brought out by Dr. Rontgen in the first instance. 

 The Physical Society of London, in its abstracts of physical papers 

 from foreign sources, classes all work with the Rontgen rays un- 

 der the head of " Light," but upon very scant grounds. Numerous 

 experiments have been made to test the character of these mysteri- 

 ous activities by the accepted criteria of light namely, reflection, 

 refraction, interference, and polarization all results being nega- 

 tive, or so slight and uncertain as to leave them still open to ques- 

 tion, and to make the name "X rays" not only the most common 

 one by which they are mentioned, but the one best suited to ex- 

 press our knowledge or ignorance of their nature. Several at- 

 tempts have been made to determine a length for them, supposing 

 them to be waves, resulting in a supposed upper limit of length 

 not greater than one hundredth that of violet light, and probably 

 not greater than one three-hundredth. In the first few months of 

 the furore of experimentation and discussion scarcely a result was 

 announced by one observer that was not controverted by another ; 

 yet out of this very contradictoriness came a rational conclusion 

 that at all events the rays are not homogeneous, but differ among 

 themselves in their properties, as do the constituent raj^s of 

 ordinary heterogeneous light. This would account for their non- 

 interference. Of refraction there is as yet no evidence, nor, so 

 far as known, is there any possibility of bringing the rays to a 

 focus and thus producing an image of any object by means of 

 them. All that can be done in that way as yet, as at first, is to 

 obtain a shadow of varying intensity by reason of the various 

 penetrability of different objects or portions of one object; and 

 so the pictures thus produced are called by various names, as 

 skiagraphs, radiographs. X-ray pictures, etc. all chosen to avoid 

 the idea that they are real light- pictures or photographs. Since 



