154 



NATURE 



\_y7inc 17, 1880 



cules, therefore, must be classed by themselves in a 

 distinct state or category. 



The same reasoning applies to two or to any number of 

 contiguous molecules, provided their motion is arrested 

 or controlled, so that no collisions occur between them ; 

 and even supposing this aggregation of isolated non- 

 colliding molecules to be bodily transferred from one part 

 of space to another, that kind of movemcr.t would not 

 thereby cause this molecular collocation to assume the 

 properties of gas ; a molecular wind may still be supposed 

 to consist of isolated molecules, in the same way as the 

 discharge from a mitrailleuse consists of isolated bullets. 



Matter in the fourth state is the ultimate result of 

 gaseous expansion. By great rarefaction the free path of 

 the molecules is made so long that the hits in a given 

 time may be disregarded in comparison to the misses, in 

 which case the average molecule is allowed to obey its 

 own motions or laws without interference ; and if the 

 mean free path is comparable to the dimensions of the 

 containing vessel, the properties which constitute gaseity 

 are reduced to a minimum, and the matter then becomes 

 e.xalted to an ultra-gaseous state. 



But the same condition of things will be produced if 

 by any means we can take a portion of gas, and by some 

 extraneous force infuse order into the apparently dis- 

 orderly jostling of the molecules in every direction, by 

 coercing them into a methodical rectilinear movement. 

 This I have shown to be the case in the phenomena which 

 cause the movements of the radiometer, and I have ren- 

 dered such motion visible in my later researches on the 

 negative discharge in vacuum tubes. In the one case the 

 heated lamp-black and in the other the electrically excited 

 negative pole supplies the force majeure which entirely or 

 partially changes into a rectilinear motion the irregular 

 vibration in all directions ; and according to the extent to 

 which this onward movement has replaced the irregular 

 motions which constitute the essence of the gaseous con- 

 dition, to that extent do I consider that the molecules 

 have assumed the condition of radiant matter. 



Between the third and the fourth states there is no 

 sharp line of demarcation, any more than there is between 

 the solid and liquid states, or the liquid and gaseous 

 states ; they each merge insensibly one into the other. In 

 the fourth state properties of matter which exist even in 

 the third state are shown c/hrct/y, whereas in the state of 

 gas they are only shown inditwtly, by viscosity and so forth. 



The ordinary laws of gases are a simplification of the 

 effects arising from the properties of matter in the fourth 

 state ; such a simplification is only permissible when the 

 mean length of path is small compared with the dimen- 

 sions of the vessel. For simplicity's sake we make ab- 

 straction of the individual molecules, and feign to our 

 imagination continuous matter of which the fundamental 

 properties— such as pressure varying as the density, and 

 so forth — are ascertained by experiment. A gas is nothing 

 more than an assemblage of molecules contemplated from 

 a simplified point of view. When we deal with pheno- 

 mena in which we are obliged to contemplate the mole- 

 cules individually, we must not speak of the assemblage 

 as gas. 



These considerations lead to another and curious specu- 

 lation. The molecule — intangible, invisible, and hard to 

 be conceived— is the only true matter, and that which we 

 call matter is nothing more than the effect upon our senses 

 of the movements of molecules, or, as John Stuart Mill 

 expresses it, "a permanent possibility of sensation." The 

 space covered by the motion of molecules has no more 

 right to be called matter than the air traversed by a rifie 

 bullet can be called lead. From this point of view, then, 

 matter is but a mode of motion ; at the absolute zero of 

 temperature the inter-molecular movement would stop, 

 and although something retaining the properties of inertia 

 and weight would remain, matter, as we know it, would 

 ■cease to exist. 



NOTES 



The Council of the Society of Artsjiave awarded the Albert 

 Medal of the Society of the present year to James Prescott 

 Joule, LL.D., D.C.L., F.R.S., "for having established, after 

 most laborious re.-^earch, the true relation between heat, electri- 

 city, and mechanical work, thus affording to the engineer a sure 

 guide in the application of science and industrial pursuits.'' 

 Tlie medal was delivered to Dr. Joule by the Prince of Wale-, 

 on Tuesday, when Sir William Thomson received the medal 

 awarded him by the Society in 1878. 



The Paris Academy of Sciences has awarded the Monthyon 

 Prize to M. Camille Flammarion for his new work entitled 

 "Astronomic Populaire." It is a large 4to volume, with mag- 

 nificent engravings, which was sold in 100 penny parts. The 

 sale in the first year of publication reached 40,000 copies. 



It is stated that M. Coggia, Astronomer to the Marseilles 

 Observatory, will be appointed Director of the Algiers Obser- 

 vatory, where no observations at all have been made since its 

 creation in 1S64 by Marshal Pelissier. 



T}[E University of Oxford has conferred the degree of D.C.L 

 on Prof. Sylve-ter and Mr. Lister, the eminent surgeon. 



On Saturday, May 5, the local committee of the French 

 Association for the Advancement of Science met at Rheims, 

 where the next meeting is to be held in August. An exposition 

 of local industry and archa;ology will be held. Arrangements 

 have been made^for excursions connected with the congress, the 

 more notable of which will be to the Han Grottoes, which are 

 situated in Belgium. Nothing has been arranged yet as to the 

 lectures to be delivered. 



The new Principal of the Royal Agricultural College, Ciren- 

 cester, the Rev. J. B. McLellan, has started a scheme of con- 

 gresses or conferences which may prove of considerable value to 

 agriculture. On Friday, the 5th inst., a goodly number of old 

 Cirencester students and professors, as well as local agriculturists, 

 met in the College Hall to discuss important agricultural ques- 

 tions. The morning session was occupied with the subject of 

 cattle diseases ; the afternoon w-as devoted to agricultural stations 

 and research. If the papers introducing the subjects were not of 

 a very high order, it may at least be conceded that the discus- 

 sions which followed brought out some sound information and 

 advice. If such congresses as this at Cirencester help to draw 

 public attention to the need for some new departure in modern 

 and scientific agricuUure, and if they stimulate those interested 

 in farming to look to the College as the central authority on a 

 subject which that institution must learn to handle adequately, 

 then we predict for them a substanial success. 



The annual conference at the Society of Arts on the laws, 

 administration and inspection with regard to public health was 

 opened on Thursday under the presidency of Mr. Stansfeld, M.P. 

 The committee had drawn up a programme of subjects for 

 discu-sion, which were grouped under the following headings : — 

 I. Administrative Organisation : 2. Amendment of the Law : 

 3. Sanitary Ins] ection and Classification of Dwellings : 4. 

 Further suggestions by Sanitary Authorities. In the discussion 

 on Thursday the chairman, in opening the proceedings, pointed 

 out the desirability of an "inquiry office" being established in 

 connection with the Local Governmeat Board, at which local 

 autliorities might obtain information based on experience. One 

 great hope for the future was that the teaching of the laws of 

 health to children was gradually spreading. The conference 

 was resumed on Friday. In reference to the third heading, the 

 following resolution was put to the meeting :—" That it is 

 expedient that the Metre politan Board of Works within the 

 metropohs, and the County Board within each county, should 



