A HISTORY OF SCIENCE 



into the glass walls, but protruding at either end for 

 attachment to the conducting wires from the induc- 

 tion coil. This tube may be mounted on a stand at a 

 height convenient for manipulation. The phospho- 

 rescence screen is usually a plate covered with some 

 platino-cyanide and mounted in the end of a box of 

 convenient size, the opposite end of which is so shaped 

 that it fits the contour of the face, shutting out the 

 light and allowing the eyes of the observer to focalize 

 on the screen at the end. For making observations 

 the operator has simply to turn on the current of elec- 

 tricity and apply the screen to his eyes, pointing it 

 towards the glowing tube, when the shadow of any 

 substance interposed between the tube and the screen 

 will appear upon the phosphorescence plate. 



The wonderful shadow pictures produced on the 

 phosphorescence screen, or the photographic plate, 

 would seem to come from some peculiar form of light, 

 but the exact nature of these rays is still an open ques- 

 tion. Whether the Roentgen rays are really a form of 

 light that is, a form of " electro-magnetic disturbance 

 propagated through ether," is not fully determined. 

 Numerous experiments have been undertaken to de- 

 termine this, but as yet no -proof has been found that 

 the rays are a form of light, although there appears to 

 be nothing in their properties inconsistent with their 

 being so. For the moment most investigators are con- 

 tent to admit that the term X-ray virtually begs the 

 question as to the intimate nature of the form of energy 

 involved. 



