36 PHYSICAL RESEARCH 



of the atomic weight of thallium. He could not 

 have had the slightest idea of the consequences of 

 these improvements when he made them. Not 

 only did they lead to his own discoveries of the 

 radiation already described ; but they made possible 

 all sorts of consequences of the greatest importance. 

 Let us mention a few: 



(a) The electric glow lamps, which are used 

 in millions and whose very existence depends upon 

 the effectiveness of the exhaustion of air. 



(b) The X-ray bulb with all its powers. 



(c) The vacuum or "thermos" flask, which 

 has made it possible to preserve liquefied gases 

 and to study their properties. This work again 

 has its important developments in pure science, in 

 the purification of materials, in the illumination 

 that has followed on the extension of our knowledge 

 of the properties of bodies at very low temperature 

 and so on. 



(d) The so-called "valve," which is greatly 

 used at the present time to multiply telephonic 

 sounds, so that they become audible. 



Let us take another of Rontgen's tools, the 

 sparking coil. Its history is not so varied as that 

 of the research on the electric discharge, but it 

 is of even greater importance, if that is possible. 

 It consists merely of two coils of wire wound on 

 the same iron core, the one having a few turns of 

 thick wire, the other many turns of thin wire. 

 Interruptions of the electric current running in the 



