SCIENCE. 



221 



Again turning on the coil the rays from the negative 

 pole fall uninterruptedly on the large end of the bulb ; 

 the dark cross is now replaced by one more intensely 

 green than the adjacent portions of the glass. The fresh 

 parts of the glass are more susceptible to luminous ex- 

 citation than the areas previously bombarded. This 

 stenciled image of the black cross, Mr. Crookes tells us, 

 is so persistent that it remained in one case after the 

 glass had been heated hot, so that the end of the bulb 

 was bent in and then blown out again. After re-exhaus- 

 tion the bright green cross came out plainly in the more 

 intense phosphorescence produced by the electrically 

 projected residual gas. Thus the molecules hammer 

 away upon the glass with sufficient energy to produce a 

 permanent impression. 



Since the molecules of the residual gas are driven vio- 

 lently from the negative pole, there should be a recoil 

 of the pole from the molecules. That such is the case 

 is shown by this electrical radiometer. The connections 

 are such that the aluminum vanes constitute the nega- 

 tive pole. The vanes are not blackened but are covered 

 on one side with mica, a non-conductor. The uncov- 

 ered sides constitute the radiating or projecting surfaces. 

 Turning on the induction current the vanes are repelled 

 and the system rotates rapidly. The phosphorescent 

 spots on the glass, produced by the impact of the mole- 

 cules projected from the vanes, rotate as the vanes do, 

 giving us a visible image of the process going on in the heat 

 radiometer. In this second form the negative pole consists 

 of a ring of platinum wire. Above this is a fly, composed 

 of mica vanes inclined like the fans of a wind-mill. Turn- 

 ing on the current the matter projected from the wire strikes 

 against the sloping vanes and sets them in motion. But 

 this is not all. I now connect a battery directly with the 

 terminals of the platinum ring, and the passage of the 

 current heats the ring red hot. Directly the fly begins to 

 turn more rapidly than before. Radiant matter is thus 

 projected by heat as well as electricity, and the ordinary 

 heat radiometer is propelled by the recoil of projected 

 radiant matter like the electrical radiometer. 



The action of magnetism on this stream of electrified 

 particles is, indeed, curious. When a straight Geissler 

 tube of low vacuum is employed it gives a narrow line of 

 violet light joining the two poles. [This tube placed over 

 the poles of an electro-magnet.] On passing the battery 

 current through the magnet underneath, the violet line is 

 repelled or attracted according I o the direction of the cur- 

 rents ; but it recovers itself after passing the magnet 

 and proceeds to the other pole. Not so with a tube of high 

 vacuum. Tlvs tube contains a mica screen, covered with 

 material which phosphoresces under molecular impact. 

 The radiant matter from the negative pole passes through a 

 narrow opening and impinges upon the screen along its 

 entire length. You observe how the phosphorescence 

 marks the path of the projected molecules. Bringing a 

 strong magnet down over the stream or actuating the 

 electro-magnet, and the luminous path curves toward the 

 side of the tube like the path of a projectile ; but in this 

 case the stream does not recover its original direct'on 

 after deflection, as in the case of the Geissler tube. This 

 same tube is fitted to determine another question of much 

 interest connected with these wonderful phenomena, ft 

 is provided with two negative projecting surfaces, and 

 the stream of molecules from each of these may be made 

 to trace its path on the mica screen in a luminous line. 

 Observe the position of this line first from one pole and 

 then the other. What now will be the result if streams 

 issue from both poles at once ? If they constitute two 

 currents of electricity in the same direction then we know 

 that they will attract each other; but if they consist of a 

 train of similarly electrified molecules, then they must 

 repel each other Put to the test of experiment we see 

 plainly that the stream lines diverge by mutual repul- 

 sion. 



We have seen that mechanical action is produced by 



the recoil from the radiant matter. It is equally true that 

 strong mechanical effects may be produced by the impact 

 of these swiftly moving molecules. This tube is ingen- 

 iously constructed with a pair of glass rails running from 

 end to end. Along them rolls freely the axle of a small 

 wheel with broad vanes as paddles. The poles are so 

 situated that the radiating molecules may strike against 

 the vanes. Turning on the induced current, the stream 

 of swiftly moving molecules strikes against the vanes on 

 one side of the wheel and sets it running along the rails. 

 Reversing the current, the wheel stops and returns on its 

 track. [Tube projected on a screen by oxy-hydrogen 

 light.] Another tube has been devised to show both 

 magnetic deflection and mechanical action on the screen. 

 The negative pole is a large, shallow cup. A mica screen 

 intercepts the converging streams of radiant matter. 



Behind the screen is placed an easily-revolving mica 

 wheel provided with vanes and making a sort of paddle 

 wheel. So arranged the molecular rays from the pole 

 are cut off from the wheel, and no movement is produced. 

 Placing a magnet over the tube the rays are deflected so 

 as to pass above the screen and the wheel begins to re- 

 volve. Reversing the magnetic poles, the deflection is in 

 the other direction, and the wheel now rotates like an 

 undershot water-wheel. Even at this high vacuum of 

 about a millionth of an atmosphere, enough matter re- 

 mains in the tube to produce a sort of molecular wind 

 under the impulsion of the negative discharge. Radiant 

 matter produces heat as well as mechanical motion when 

 its motion is arrested. The negative pole in this tube is 

 a cup or concave projector. The radiant matter comes 

 to a focus near the cup and then passes on toward the 

 other end of the tube. But on bringing a magnet near it 

 the stream of radiant matter is deflected so as to strike 

 the side of the tube, producing a green, phosphorescent 

 spot. The nearer the magnet approaches the greater the 

 deflection ot the stream and the smaller the spot. Cov- 

 ering the side of the tube with wax and placing it in front 

 of the lantern, a dark image of the tube is projected be- 

 cause of the opaque wax. But with the coil in action 

 the approach of the magnet deflects the radiant stream, 

 the tube is heated by the impact of the molecules, the 

 wax melts and becomes transparent, and the light trom 

 the lantern passes through. 



The heat generated by the arrest of radiant matter is 

 further shown by a bulb of special device. It has a negative 

 pole of aluminum in the form of a concave projector. 

 In its focus is fixed a piece of platinum foil. Turning 

 on the coil, the projected molecules impinging against 

 the platinum at last raise it to a red heat. Indeed Mr. 

 Crookes has actually melted iridio-platinum in such a 

 focus. We are accustomed to see powerful heating 

 effects produced by currents of electricity traversing 

 rather poor conductors ; but here red hot platinum glows 

 with the invisible cannonade of innumerable molecules 

 of the air we breathe. 



These effects take place indifferently with hydrogen, 

 carbonic acid gas, and air at this high vacuum. The 

 only difference appears to be that the phosphorescence 

 begins at different pressures with the different gases. 

 The results obtained depend, therefore, not on chemical 

 properties, but on the physical, molecular condition of 

 the gaseous residues. These phenomena are so entirely 

 different from those obtained at ordinary degrees of ex- 

 haustion, that Mr. Crookes appears to me to be justified 

 in considering that he has at last verified Faraday's early 

 hypothesis of matter in a radiant state. Mr. Crookes has 

 well said that, " In studying this fourth state of matter we 

 seem at length to have within our grasp and obedient to 

 our control the little indivisible particles which, with 

 good warrant, are supposed to constitute the physical 

 basis of the universe. We have seen thit in some of its 

 properties radiant matter is as material as this table, 

 while in other properties it almost assumes the character 

 of radiant energy. We have actually touched the 



