March 4, 1875] 



NATURE 



359 



The portion of the hypothetical curve from C io E represents 

 states which are essentially unstable, and which cannot therefore 

 be realised. 



Now let us suppose the medium to pass from B io !• along 

 the hypothetical curve B C D E F in a state always homo- 

 geneous, and to return along the straight line EB in the form of 

 a mixture of liquid and vapour. Since the temperature has 

 been constant throughout, no heat can have been transformed 

 into work. Now the heat transformed into work is representet^ 

 by the excess of the area EDEover B CD. Hence the condi- 

 tion which determines the maximum pressure of the vapour at 

 given temperature is f- n the line BE cuts off equal areas from 

 the curve above an;! l>;lov,'. 



The higher the temperature, the greater the part of the pres- 

 sure which dejjends on motion, as compared with that which 

 depends on forces between the particles. Hence, as the tempe- 

 rature liscs, the dip in the curve becomes less marked, and at a 

 certain temper^.ture the curve, instead of dipping, merely becomes 

 horizontal at a certain point, and then slopes upv;ard as before. 

 This point is called the critical point. It has ijeen determined 

 for carbonic acid by the masterly researches of Andrews. It 

 corresponds to a definite temperature, pressure and density. 



At higher temperatures the curve slopes upwards throughout, 

 and there is nothing corresponding to liquefaction in passing from 

 the rarest to the densest state. 



The molecular theory of the continuity of the liquid and 

 gaseous states forms the subject of an exceedingly ingenious 

 thesis by Mr. Johannes Diderik van der Waals, * a gi'aduate of 

 Leyden. There are certain points in which I think he lias fallen 

 into mathematical errors, and his final result is certainly not a 

 complete expression for the interaction of real molecules, but 

 his attack on this difficult question is so able and so brave, that 

 it cannot fail to give a notable impulse to molecular science. It 

 has certainly directed the attention of more than one inquirer to 

 the study of the I.ow-Dutch language in which it is written. 



The purely thermodynamical relations of the different states 

 of matter do not belong to our subject, as they are independent 

 of particular theories about molecules. I must not, however, 

 omit to mention a most important American contribution to this 

 part of thermodynamics by Prof. Willard Gibbs,t of Yale Col- 

 lege, U.S., who has given us a remarkably simple and thoroughly 

 satisfactory method of representing the relations of the different 

 states of matter by means of a model. By means of this model, 

 problems which had long resisted the efforts of myself and others 

 may be solved at once. J. Cleric -Maxwell 



{To be continued.) 



SOCIETIES AND ACADEMIES 

 London 



Geological Society, Feb. 19. — Annual General Meeting. — 

 i\lr. John Evans, V.P.R.S., president, in the chair. — The Secre- 

 tary read the reports of the Council and of the Library and 

 Museum Committee. The general position of the Society was 

 described as satisfactory, although, owing to extraordinary 

 expenses during the year, the excess of income over expenditure 

 was but small in comparison with former years. The Society 

 was said to be prosperous, and the number ot Fellows to be 

 rapidly increasing. 



In presenting the Wollaston Gold Medal to Prof, de Koninck, 

 of Liege, F.M.G.S., the President addressed him as follows :— 

 " Monsieur le Docteur de Koninck, it is my pleasing duty to 

 place in your hands the Wollaston Medal, which has been 

 awarded to you by the Council of this Society in recognition of 

 your extensive and valuable researches and numerous geological 

 publications, especially in Carboniferous Paleontology. These 

 researches are so well known, and have gained you so world- 

 wide a reputation, that I need say no more than that your 

 paIa:ontological works must of necessity be almost daily consulted 

 by all who are interested in the fauna of the Carboniferous 

 period. Already in 1853 the numerous and able Pal^onto- 

 logical works which you had published in the preceding twenty 

 years had attracted the grateful notice of the Council of this 



* Over dc continuiteit van den fas en vloeistof toestand. Leiden : A. W. 

 Sijthofr, 1873. 



+ " A method of gecraettical representation of the thermodynamic pro- 

 perties of substances by means of surfaces." Transactions of the Connec- 

 ticut Academy of Arts and Sciences, Vol. ii. Part 2. 



Society, who in that year begged you to accept the balance of 

 the proceeds of the Wollaston Fund, in aid of the publication 

 of your work on Encrinites, then in progress. It was m the 

 same year that the Society had the satisfaction of electmg you a 

 Foreign Member of their body ; and now, after a second period 

 of rather more than twenty years devoted to the study not only 

 of geology and pala-ontology, but also of chemical analysis, I 

 have the pleasure of conferring upon you the highest additional 

 honour it lies in the power of this Society to bestow, by present- 

 ing you with the medal founded by the illustrious Wollaston, 

 who was himself also a chemist as well as a geologist. If any' 

 thing could add to the satisfaction we feel in thus bestowing the 

 medal, it is your presence among us this day, which will enable 

 you more fully to appreciate our unanimous sense of the hit^h 

 value of your labours in the cause which Me all have at heart.'"' 



The President then presented the balance of the proceeds of 

 the Wollaston Donation Fund to Mr. L. C. Miall, of Leeds 

 and addressed him in the following terms : — "Mr. Miall I have 

 much pleasure in presenting you with the balance of the pro- 

 ceeds of the Wollaston Fund, which has been awarded ycu by 

 the Council of this Society to assist you in your researches on 

 Fossil Reptilia. Those who had the good fortune to be present 

 at the meeting of the British Association at Bradford in 1873, 

 and to hear the masterly report of the Committee on the Laby- 

 linthodonts of the Coal-measures, drawn up by yourself, and 

 those also who have studied the papers which you have communi- 

 cated to this Society on the Remains of Labyrinthodonta from 

 the Keuper Sandstone of Warwick, must be well aware of the 

 tliorough and careful nature of your researches, carried on, I 

 lidieve, in a somewhat isolated position, and remote from those 

 aids which are so readily accessible in the metropolis and some 

 I f our larger towns. I trust that the proceeds of this fund 

 ^vhich I have now placed in your hands will be regarded as a 

 testimony of the interest which this Society takes in your labours, 

 and may also prove of some assistance to you in si ill further 

 prosecuting them." 



Mr. Miall, in rj-ply, said that he felt that his sincere thanks 

 were due to the Geological Society for awarding liim the balance 

 of the proceeds of the Wollaston Donation Fund as a token of 

 appreciation of the little work that he had been able to do, and 

 also to the President for the terms in which he had been kind 

 enough to speak of him. He should regard this donation, not 

 only as an honour received by him, but also as a trust to be 

 expended to the best of his power in accordance with the 

 intentions with which it had been conferred upon him by the 

 Society. 



The President next handed the Miuchison Medal to Mr. 

 David Forbes for transmission to Mr. W. J. Kenwood, F.R.S., 

 and spoke as follows: — "Mr. 'David Forbes, in placing the 

 Murchison Medal and the accompanying cheque in your hands 

 to be conveyed to our distinguished Fellow, Mr. \\'illiam Jory 

 Henwood, I must request you to express to him our great regret 

 that he is unable to attend personally to receive it. His re- 

 searches on the metalliferous deposits, not only of Cornwall and 

 Devonshire, but of Ireland, Wales, North-western India, North 

 America, Chili, and BrazU, extending as they do to questions of 

 subterranean temperature, electric cun-ents, and the quantities of 

 water present in mines, are recorded in memoirs which form 

 text-books for mining students. They have for the most part 

 been contributed to the Royal Geological Society of Cornwall, 

 which has taken a pride in publishmg them ; but I trust that it 

 will be a source of satisfaction to Mr. Henwood, after fifty years 

 of laborious research, and amidst the physical suffering caused 

 by a protracted illness, to receive this token of appreciation at 

 the hands of another Society which takes no less interest in the 

 subjects of his investigations." 



Mr. David Forbes said that in receiving the Murchison Medal, 

 on behalf of Mr. W. J. Henwood, he was commissioned by that 

 gentleman to express his great regret that the bad state of his 

 health and his advanced age prevented his appearing in person 

 to thank the Council for the high honour they had 'conferred 

 upon him, and the extreme gratification he felt in finding that 

 the results of his labours in the investigation of the phenomena 

 of mineral veins, which had extended over more than fifty years, 

 had thus been recognised by the Geological Society of London. 



The President then presented to Prof. H. G. Seeley the 

 balance of the Murchison Geological Fund, and said : — " Mr. 

 Seeley, your researches in geology and on fossil osteology have 

 already extended over a period of upwards of sLxteen years, and 

 the numerous and valuable essays which you have contri- 

 buted to the Annals and Magazine of Natural History, as well 



