158 Mr. William Crookes on Molecular Physics, d'c. [April 4, 



will not produce any movement. I now put a magnet, g, over the tube, 

 so as to deflect the stream over or under the obstacle c d, and the result 

 will be rapid motion in one or the other direction, according to the 

 way the magnet is turned. I now throw the image of the apparatus on 

 the screen. The spiral lines painted on the wheel show which way it 

 turns. I arrange the magnet to draw the molecular stream so as to 

 beat against the upper vanes, and the wheel revolves rapidly, as if it 

 were an over-shot water-wheel. I now turn the magnet so as to drive 

 the molecular stream underneath ; the wheel slackens speed, stops, and 

 then begins to rotate the other way, as if it were an under-shot water- 

 wheel. This can be repeated as often as I like to reverse the position 

 of the magnet, the change of rotation of the wheel showing imme- 

 diately the way the molecular stream is deflected. 



This experiment illustrates the last of the phenomena which time 

 allows me to bring before you, attending the passage of the induc- 

 tion spark through a highly exhausted atmosphere. It will now be 

 naturally asked. What have we learned from the phenomena described 

 and exhibited, and from the explanations that have been proposed ? 

 We find in these phenomena confirmation of the modern views of 

 matter and energy. The facts elicited are in harmony with the theory 

 that matter is not continuous but composed of a prodigious number of 

 minute particles, not in mutual contact. The facts also are in full 

 accordance with the kinetic theory of gases — to which I have already 

 referred — and with the conception of heat as a particular kind of energy, 

 expressing itself as a rapid vibratory motion of the particles of matter. 

 This alone would be a lesson of no small value. In Science, every 

 law, every generalisation, however well established, must constantly 

 be submitted to the ordeal of a comparison with newly-discovered 

 phenomena ; and a theory may be pronounced triumphant when it is 

 found to harmonise with and to account for facts which when it was 

 propounded were still unrecognised or unexplained. 



But the experiments have shown us more than this : we have been 

 enabled to contemplate matter in a condition hitherto unknown, — in a 

 fourth state, — as far removed from that of gas as gas is from liquid, 

 where the well-known properties of gases and elastic fluids almost 

 disappear, whilst in their stead are revealed attributes previously 

 masked and unsuspected. In this ultra-gaseous state of matter 

 phenomena are perceived which in the mere gaseous condition are as 

 impossible as in liquids or solids. 



I admit that between the gaseous and the ultra-gaseous state there 

 can be traced no sharp boundary ; the one merges imperceptibly into 

 the other. It is true also that we cannot see or handle matter in this 

 novel phase. Nor can human or any other kind of organic life con- 

 ceivable to us penetrate into regions where such ultra-gaseous matter 

 may be supposed to exist. Nevertheless, we are able to observe it and 

 experiment on it, legitimately arguing from the seen to the unseen. 



Of the practical applications that may arise out of these researches, 

 it would now be premature to sj)eak. It is rarely given to the dis- 



