634 SCIENCE PROGRESS 



parties brought him world-wide fame. After his discovery he 

 was appointed professor of experimental physics and director 

 of the Physical Institute at Munich, a post from which he 

 resigned only in 1919. His work was honoured in England 

 by the award of the Rumford Medal of the Royal Society 

 (jointly with Prof. P. Lenard) in 1896. In 1901 he received 

 the Nobel Prize for Physics. Previous to his discovery of 

 X-rays he carried out research in many different branches 

 of Physics, including elasticity, capillarity, the conduction of 

 heat through crystals, the ratio of the specific heats of gases, 

 the electromagnetic rotation of polarised light, etc. 



X-rays had really been detected before Rontgen's investiga- 

 tions by Hertz and by Lenard, who placed an aluminium 

 window opposite the cathode of an exhausted tube and ob- 

 tained rays in the air outside which affected a photographic 

 plate placed in their path. Lenard stated, however, that these 

 rays were deflected by a magnetic field and, in consequence, 

 he identified them with the cathode rays. Rontgen's dis- 

 covery resulted from his observation that a barium platino- 

 cyanide screen fluoresced when placed near a Crooke's tube 

 (of the type used to demonstrate the shadow cast by the 

 cathode stream) even when the tube was covered with black 

 paper. He investigated the phenomenon very thoroughly for 

 several months, and towards the end of 1895, published a 

 paper in the Sitzungsberichte der Wurzburger Physik-medic 

 Gesellschaft (translated in Nature, 1896) which contained a 

 description of all the simpler and well-known properties of the 

 rays with the exception of their effect on the electrical con- 

 ductivity of air. In particular it was shown that the rays 

 are produced by the impact of the cathode rays on the glass 

 walls of the exhausted tube and that they are not reflected 

 or refracted {e.g. by prisms of water or glass, etc.) as light 

 rays are. Rontgen was thus led to abandon his original idea 

 that the rays could be classed with ultra-violet light, and 

 suggested that perhaps they might be longitudinal aether waves. 



The announcement of the discovery created enormous 

 interest in the daily press as well as in scientific circles. The 

 first public demonstration in this country would appear to have 

 been that given by A. W. Porter at University College, London, 

 on January 30, 1896, with a Crooke's focus tube, i.e., a tube 

 with a concave cathode which focused the cathode stream 

 on a sheet of platinum held in the centre of the bulb. The 

 photographs obtained with this tube were much sharper than 

 those obtained by Rontgen and, in a discussion which took 

 place at the Royal Society on February 13 after J. J. Thomson 

 had described the effect of the rays on the conductivity of air. 

 Porter gave an account of an experiment which showed that the 



