22 K.r.IXOIS ACADIiMY OF SCIENCE. 



chemistry. During- this period, which lasts, with very httle 

 change, to the present time, the attempt to connect the forces 

 which hold the atoms in combination with electrical forces in any 

 definite way was almost completely abandoned. It is true that 

 the terms "positive" and "negative" have been frequently used 

 throughout the period, but they have been used in a wholly vague 

 and indefinite way, with no real thought of electrical properties in 

 the groups. 



As so often happens, the beginning of a return to an electrical 

 theory of combination came from the study of phenomena in a 

 different and, as it seemed at the time, wholly unrelated field. 

 During the late seventies, Crookes busied himself with the study 

 of electrical discharge through highly rarefied gases. The phe- 

 nomena which he discovered were so strange and startling that 

 he spoke freely of a "fourth state" of matter. The physicists 

 and chemists of the time were disposed to look on the expression 

 as somewhat sensational, but the event has shown that he was 

 nearer right than his critics. The phenomena of most interest to 

 us are those of the discharge from the cathode, or negative pole, 

 through a tube in which the pressure of the residual gas has been 

 reduced to one-millionth of an atmosphere. Under such condi- 

 tions rays are shot out in straight lines perpendicular to the sur- 

 face of the cathode and when they impinge on the glass opposite 

 they produce a beautiful green fiuorcscence and give rise to the 

 X-rays, though those rays were not discovered till some fifteen 

 years later. Crookes showed that this "radiant matter," as he 

 called it, almost with the vision of a prophet, travels straight 

 across the tube, irrespective of the location of the anode. He 

 showed that an opaque object in its path will cast a sharp shadow 

 on the fluorescent glass; he showed that if it strikes the vanes 

 on one side of a little wheel suspended in its })ath the wheel will 

 rotate, and he showed that it can be deflected by a magnet. He 

 found, too, that this radiant matter came always from the negative 

 ])ole, never from the positive. He had discovered a stream of 

 electrons, but the world had to wait some fifteen years before the 

 X-rays emanating from the fluorescent glass were discovered, and 

 nearly twenty years before the real properties of the electrons 

 were established. 



Meanwhile, during the eighties, the ionization theory of Arrhe- 

 nius was proposed, and with Ostwald as its Nestor, gained rapidly 

 in favor until it has become to-day the only logical basis which we 

 have for the accurate discussion of the properties of solutions. 



