274 CATHODE KAYS AND RONTGKEN KAYS. 



faction is of a moderate degree, when the vacuum is maintained at a few 

 hundredths, or at most a few thousandths of an atmosphere. One must 

 not be contented with this degree of exhaustion if it is desired to study 

 the cathode rays. It is necessary to go further, as did Lenard and 

 Crookes, without, however, going too far. The English physicist, in 

 particular, pushed the exhaustion to a prodigious degree. In the 

 Crookes tube>. so called, the pressure is only one millionth of an 

 atmosphere. The pressure of the remaining gas valued in millimeters 

 of mercury does not reach more than 0.00076. The English scientist 

 claimed that when exhausted to this point the residue no longer has 

 the properties of ordinary gases; according to him it is a hypergas as 

 different from the true gaseous state as the latter is from the liquid 

 state, and forming a fourth condition of matter, following the liquid, 

 the solid, and the gas proper; this he called radiant matter. Crookes, 

 relying on what the kinetic theory teaches with reference to the con- 

 stitution of gases, desired to determine the nature of this fourth state 

 of matter. In reality, the gas. rarefied to the millionth of an atmos- 

 phere, has not acquired, by this fact alone, an entirely new character; 

 but it has acquired it most certainly when electrification is added to 

 the rarefaction, and it is then that it constitutes the emanation or the 

 cathode ray. 



We have said that the vacuum must not be pushed too far. if one 

 goes beyond the millionth of an atmosphere — and the perfection 

 of mechanism allows going much further than that — the gaseous 

 idue can not be electrified; electricity will not pass through; there 

 \onger a current. The electric force is incapable of penetrating 

 e vacuum; this resistance of the vacuum to the passage of elec- 

 ts an article of faith among physicists, especially since the 

 nents of Walsh, of Morren, and of Schultz. The importance of 

 rinciple is very great from the theoretical point of view; it fur- 

 ,. in fact, a new test for matter. But in its application its prac- 

 ..v.. calue is very restricted. The experiments of Lenard. after those 

 of Hertz in showing us the propagation of certain forms of electricity 

 in vacuo, instruct as to the nature of these restrictions. We shall 

 say. with J. Perrin, that it is very probable thai recognizable elec- 

 tricity which can be experimentally detected can not propagate itself 

 without a material support, but this is not certain. 



If now we return to Crookes's tube, in which the vacuum has been 

 pushed to one millionth, we shall see that the current behaves itself 

 rather differently from what it does in the tubes where the rarefaction 

 is less. The path of the current has lost much of its brilliancy: it no 

 longer appears as an uncertain glow, wavering, striated, of a hue inter- 

 mediate between rose and violet. All the remainder of the interior 

 of the bulb remains dark. The electricity passes again and follows 



