THE DISCOVERY OF RONTGEN. 191 



able to find gall-stones and other injurious bodies whose discovery 

 is, at present, attended with great difficulty. 



The following observations help to explain how the image on 

 the sensative gelatine plate is produced. Rontgen observed that 

 even when he enclosed the vacuum tube in a dark box of paste- 

 board, a screen overlaid with barium cyanide of platinum began 

 to phosphoresce as soon as the elecric current passed through the 

 tube. The astonishing phenomenon that invisible rays producing 

 phosphorescence passed through the black pasteboard box, induced 

 Rontgen to try other materials, and he found that certain salts of 

 lime, mineral salt, ordinary glass, also phosphoresced. It is there- 

 fore probable that the photographic image on the plate is produced 

 by the phosphorescence of the glass, or perhaps, of the gelatine, 

 which flames up the more vivaciously the more the object before 

 the dark-slide, which lets pass the X rays, is penetrable. 



Professor Conrad Rontgen was born at Lennep, March 27th, 

 1845. ^^ December, 1870, he became assistant at the Physical 

 Institute of Wurzburg, where he remained till May, 1872, and then 

 went as assistant to the Physical Institute of Strassburg. A year 

 after he was appointed professor at the Academy of Hohenheim. 

 In 1876 we find him at Giessen, and in 1888 he became director 

 of the Physical Institute of the University of Wurzburg. He has 

 published many scientific essays, which are the results of much 

 study and research. 



When the Emperor William II. heard of this important dis- 

 covery he ordered Rontgen to come to Berlin, where he performed 

 his experiments before His Majesty, who presented him with a high 

 decoration (Krunenorden) for the great service he had rendered to 

 science, the full results of which cannot yet be ascertained. 



Good Liquid Cement. — The following is said to make an 

 excellent liquid cement : — To a solution of chloral hydrate in 

 water dissolve gelatine to the required consistency. The cement 

 thus made is said to have great adhesiveness and to remain indefi- 

 nitely unchanged. Ordinary glue may be used instead of the 

 more expensive gelatine ; it is equally strong. 



