484 



NATURE 



IScpt. 



18S0 



The quite independent confirmation of my discovery of the 

 limit of the liquid state given m a letter in Nature, vol. xxii. 

 p. 435, by my old colleague, Dr. Carnelley, helps to dispel the 

 idea of an intermediate state above the critical point, and con- 

 firms me in the use of the term "gas " for all fluids above their 

 critical temperatures in speakins; of the "solubility of solids in 

 gases." The term vapour should only be applied to an aeriform 

 fluid which by pressure alone can be reduced to the solid or 

 liquid state, and above the critical temperatiire this cannot be 

 done. As yet I have no evidence that vapours so defined arc 

 capable of dissolving solids, and this negative property may help 

 to form a defmitiou of that division of matter. As Dr. Carnelley 

 does not mention the coincidence of our researches, perhaps you 

 will permit me to quote from our respective papers. Dr. Car- 

 nelley says: — i. "In order to convert a gas into a liquid, the 

 lemperaliirc must be hclow a certain point (termed by Andrews 

 the critical Uiiipcrature of the substance), otherwise no amount 

 of pressure is capable of liquefying the gas." 



As far back as May 24 I wrote (" On the State of Fluids at 

 their Critical Temperatures," Proc. Roy. Soc. No. 205, 1880) : — 

 " The same results were obtained as before. When the tempe- 

 rature was below the critical point, the contents of the tube were 

 liquid, and when over that temperature the reaction was always 

 gaseous, notwithstanding the variations of pressure. 

 . "I tliinlc we have in these experiments evidence that the liquid 

 state ceases at the critical temperature, and that pressure will not 

 materially alter the temperature at which the cohesion limit 

 occurs." Dr. Carnelley will find the whole of my paper devoted 

 to an experimental demonstration of what he has now deduced 

 from his experiments. The paper was written with the title, 

 "On the Cohesion Limit," but by the advice of Sir William 

 Thomson, to whose great kiiidnes; in helping me with advice 

 and information I am much indebted, I altered the title until I 

 had the whole field explored. This I have since done, and have 

 completely established the "cohesion limit" for all liquids — that 

 for homogeneous liquids being an isotherm starting from the 

 critical point. My paper being a veiy full one has taken much 

 time and work, and the corrections fcr over a thousand experi 

 ments will take me some time yet. Prof. Stokes (whose kindly 

 i nterest and encouragement have greatly lightened my labours) 

 has been kept informed of my progress, and is cognisant of the 

 work I have done in this direction. Dr. Carnelley's second 

 conclusion is also very interesting, especially when applied to 

 water ; but surely we are not to understand that the solid ice 

 was hot throughout, or that, if a thermometer had been imbedded 

 in the ice, it would have risen. Although the vessel be red hot, 

 the ice need never be allowed to melt, but made to pass directly 

 into vapour, and yet its temperature reinain 0° till it has been 

 entirely volatilised. 



I notice from your report of the British Association that Sir 

 William Thomson calls attention to Cagniard de Latour's method 

 of showing the critical state of a liquid by sealing the requisite 

 proportion of liquid in a stout tube and heating it in a bath. It 

 should not be forgotten that, although to Dr. Andrews un- 

 doubtedly belongs the credit of establishing the definite finish of 

 the boiling-line and the apparent continuity of the liquid and 

 gaseous states, to Baron Cagniard de Latour belongs the 

 discovery of "I'etat partieulier" where the liquid state ends. 

 Latour's method, although often used by Mr. Hogarth and 

 myself, is not convenient for purposes of research. The method, 

 your report goes on to say, was criticised by Prof. W. Ramsay, 

 in what spirit we are not informed, but Dr. Ramsay added that 

 he had found an apparatus in which a screw was employed to 

 produce increase of pressure instead of using the expansion 

 of the lir|uid itself. Dr. Ramsay, however, did not say 

 whether the apparatus he had found was that invented by Mr. 

 Hogarth and myself, and described by us in Proc. Roy. Soc, 

 No. 201, iSSo, in which india-rubber in a hollow cap is made 

 by compression to yield a perfectly tight joint and to answer also 

 for a screw wdien protected by a facing of leather. Dr. Ramsay 

 visited my laboratory, and had the apparatus taken down and 

 fitted up before his eyes, and with my permission had an appa- 

 ratus made. The use of the compressed india-rubber for obtain- 

 ing the requisite close fitting constitutes the important feature of 

 my apparatus ; the employment of iron for constructing the 

 vessel enabling experimenters to dispense with the use of two 

 liquids as in Andrews' apparatus — mercury being used alone. 



I have made some little progress with the construction of 

 vessels to withstand pressure at high temperatures, and I expect 

 m a few weeks (when I have prospect of leisure) to carry my 



crystallisation experiments to a scientific if not commercial 

 success. J, B_ hankay 



Private Laboratory, Sword Street, Glasgow 



Fascination 



I EXPECTED some of your readers to refute the explanation of 

 Mr. Stabbing on "Fascination." I see in Nature, vol. xxii. 

 )i. 3S3 another paragraph which is not more to the purpose. 

 Want of presence of mind and stupefaction are not fascination, 

 In 1S59 (twenty-one years ago) I followed in the rocks of Avon. 

 close by the park of Fontainebleau, the fairy paths of Denecourt, 

 when the approach of a storm induced me to leave the blue 

 arrows, indicating the right path, for a short cut. I soon lost 

 my way, and found myself in a maze of brambles and rocks, 

 when I was startled by seeing on my left hand, at a distance of 

 about ten yards, a snake, whose body lifted up from the ground 

 at a height of about a yard, was swinging to and fro. I 

 remained motionless, hesitating whether to advance or to retreat, 

 but soon perceived that the snake did not mind me, but kept on 

 maintaining its swinging motion, and some plaintive shrieks 

 attracted my attention to a greenfinch perched on a branch of a 

 young pine overhanging the snake, with his feathers ruffled, 

 following by a nod of his head on each side of the branch the 

 motions of the snake. He tottered, spread his wings, alighted 

 on a lower branch, and so on untd the last branch was reached. 

 I then flung my stick at the snake, but the point of a rock 

 broke it and the snake disappeared with the rapidity of an 

 arrow. On approaching the spot, a real abode of vipers, which 

 I did with the greatest precaution, knowing by observation that 

 death may be the result of the bite of a viper, I saw the green- 

 finch on the ground agitated by convulsive and spasmodic 

 motion, opening and shutting his eyes. I put him in my bosom 

 to try the effect of heat, and hastened to reach the park of 

 Fontainebleau. The little claws of the bird opening and 

 shutting, perhaps as an effect of heat, made me think that he 

 might perhaps be able to stand on my finger, and he did clutch 

 it, and held on with spasmodic squeezes. In the park I got 

 : ome water, and made him drink it. In short, he revived and 

 finally flew off in the lime-trees of the park. 



Now whilst following the motions of the snake and bird I ex- 

 perienced a singular sensation. I felt giddy ; a squeezing like 

 rat iron hoop pressed in my temples, and the ground seemed to 

 me to be heaving up and down. In fact the sensation was quite 

 analogous to that experienced on a beginning of sea-sickness. 



Fro n these facts would it not seem probable that fascination is 

 nothing more nor less than an extreme fatigue of the optic nerve, 

 jjroduced by a rapid gyratory motion of a shining object and 

 resulting in a nervous attack and a coma ? Curiosity rivets at 

 first the attention of the bird, unconscious of any danger, and 

 when giddiness warns him of his peril it is too late. The snake 

 is as well aware of this as the Lophius piscaiorius is of the effect 

 of his membrane. 



In this system the fact of the bird coming down from a higher 

 to a lower branch would be explained by the supposition that, 

 giddiness overtaking him, he opened iuitinctively his wings and 

 clung to the next support that he found, the motion having 

 partially removed the giddiness so as to enable him to hold fast. 



Observe, that nothing hindered the bird from flying away, and 

 that the snake being at most five feet long, could never have 

 reached even the lowest branch. 



Besides he could have no nest to protect, for in the rocks of 

 Avon there is no water save rain-water in the hollows of the 

 rocks, and this is not potable on account of microscopic leeches 

 which people it, the instinct of birds teaching them to avoid it. 



Jersey, August 29 C11.A.TEL 



P.S. — I inquired of Mr. Denecourt, " the sylvan of the forest," 

 if he were aware of the existence of such large snakes in the 

 forest, and he told me that he had only seen, in the " rocher 

 Cuvier ChatiUon," a snake about four and a half feet long, which 

 he killed, but that even larger snakes had been seen in this very 

 "rocher d'Avon " and in the "rocher St. Germain," but he 

 thought that they were only " couleuvres " of a large size and 

 quite inoffensive. 



Meteor 



On the 19th inst., at 11.34 P-™- (within aminute of G.M.T.), 

 I observed a large meteor in the east, towards which I happened 

 to be looking, the sky being quite free from clouds, and clear. 



