June 17, iSSo] 



NATURE 



153 



between flat disks on a scale of 10 centims. for a milli- 

 metre and 5 centims. to t,ooo cells. 



From the curve thus laid down the following numbers 

 were deduced : — ■ 



The remainder of the paper is chiefly occupied withthe 

 study of the phenomena of the electric arc under various 

 conditions of distance, pressure, and potential ; the 

 results obtained support the view that the arc and the 

 stratified discharge are merely modifications of the same 

 phenomenon. 



{.To be contimied^ 



A FOURTH STATE OF MATTERS 



IN introducing the discussion on Mr. Spottiswoode and 

 Mr. Moulton's paper on the " Sensitive State of 

 Vacuum Discharges," at the meeting of the Royal Society 

 on April 15, Dr. De La Rue, who occupied the chair, 

 good-naturedly challenged me to substantiate my state- 

 ment that there is such a thing as a fourth or ultra-gaseous 

 state of matter. 



I had no time then to enter fully into the subject ; nor 

 was I prepared, on the spur of the moment, to marshal 

 all the facts and reasons which have led me to this con- 

 clusion. But as I find that many other scientific men 

 besides Dr. De I-a Rue are in doubt as to whether matter 

 has been shown to exist in a state beyond that of gas, I 

 will now endeavour to substantiate my position. 



I will commence by explaining what seems to me to be 

 the constitution of matter in its three states of solid, 

 liquid, and gas. 



I. First as to Solids : — These are composed of discon- 

 tinuous molecules, separated from each other by a space 

 which is relatively large — possibly enormous — in com- 

 parison with the diameter of the central nucleus we call 

 tiiokciilc. These molecules, themselves built up q,{ atoms, 

 are governed by certain forces. Two of these forces 1 

 will here refer to — attraction and motion. Attraction 

 when exerted at sensible distances is known as gravita- 

 tion, but when the distances are molecular it is called 

 adhesion and colicsion. Attraction appears to be inde- 

 pendent of absolute temperature ; it increases as the 

 distance between the molecules diminishes ; and were 

 there no other counteracting force the result would be a 

 mass of molecules in actual contact, with no molecular 

 movement whatever — a state of things beyond our con- 

 ception — a state, too, which would probably result in the 

 creation of something that, according to our present 

 views, would not be matter. 



This force of cohesion is counterbalanced by the move- 

 ments of the individual molecules themselves, movements 



» " On a Fourth State of Matter 

 Society. By W. Crookes, F.R. S. 



1 a letter to the Secretary of the Royal 



varying directly with the temperature, increasmg and 

 diminishing in amplitude as the temperature rises and 

 falls. The molecules in solids do not travel from one 

 part to another, but possess adhesion and retain fixity of 

 position about their centres of oscillation. Matter, as we 

 know it, has so high an absolute temperature that the 

 movements of the molecules are large in comparison with 

 their diameter, for the mass must be able to bear a 

 reduction of temperature of nearly 300^ C. before the 

 amplitude of the molecular excursions would vanish. 



The state of solidity, therefore— the state which we are 

 in the habit of considering /r?;- excellence as that of matter 

 — is merely the effect on our senses of the motion of the 

 discrete molecules among themselves. 



Solids exist of all consistences, from the hardest metal, 

 the most elastic crystal, down to thinnest jelly. A perfect 

 solid would have no viscosity, i.e., when rendered discon- 

 tinuous or "divided by the forcible passage of a harder 

 solid, it would not^ close, up behind and again become 

 continuous. 



In solid bodies the cohesion varies according to some 

 unknown factor which we call chemical constitution ; 

 hence each kind of solid matter requires raising to a dif- 

 ferent temperature before the oscillating molecules lose 

 their fixed position with reference to one another. At 

 this point, varying in different bodies through a very wide 

 range of temperature, the solid becomes liquid. 



II. In liquids the force of cohesion is very much re- 

 duced, and the adhesion or the fixity of position of the 

 centres of oscillation of the molecules is destroyed. When 

 artificiaUy heated, the inter-molecular movements increase 

 in proportion as the temperature rises, until at last cohe- 

 sion is broken down, and the molecules fly off into space 

 with enormous velocities. 



Liquids possess the property of viscosity— that is to say, 

 they ofTer a certain opposition to the passage of solid 

 bodies ; at the same time they cannot permanently resist 

 such opposition, however slight, if continuously apphed. 

 Liquids vary in consistencv from the hard, brittl", appa- 

 rently solid pitch to the lightest and most ethereal liquid 

 capable of existing at any particular temperature. 



The state of liquidity, therefore, is due to inter-m.olecu- 

 lar motions of a larger and more tumultuous character 

 than those which characterise the solid state. 



III. In gases the molecules fly about in every conceiv- 

 able direction, with constant collisions and enormous and 

 constantly varying velocities, and their mean free path is 

 sufficiently great to release them from the force of adhe- 

 sion. Being free to move, the molecules exert pressure 

 in all directions, and were it not for gravitation they 

 would fly off into space. The gaseous state remams so 

 long as the collisions continue to be almost infinite in 

 number, and of inconceivable irregularity. The state of 

 caseity, therefore, is preeminently a state dependent on 

 collisions. A given space contains millions of milhons of 

 molecules in rapid movement in all directions, each mole- 

 cule having millions of encounters in a second. In such 

 a case the length of the mean free path of the molecules 

 is exceedingly small compared with the dimensions of the 

 containing vessel, and the properties which constitute the 

 ordinary gaseous state of matter, which depend upon 

 constant collisions, are observed. 



What, then, are these molecules ? Take a single lone 

 molecule in space. Is it sohd, liquid, or gas? Solid it 

 cannot be, because the idea of solidity involves certain 

 properties which are absent in the isolated molecule. In 

 fact, an isolated molecule is an inconceivable entity, 

 whether we try, like Newton, to visualise it as a little 

 hard spherical body, or, with Boscovich and Faraday, to 

 regard it as a centre of force, or accept Sir "William 

 Thomson's vortex atom. But if the individual molecule 

 is not solid, a fortiori it cannot be regarded as a liquid or 

 CTas for these states are even more due to inter-molecular 

 collisions than is the solid state. The individual mole- 



