48o 



NA TURE 



[September 7, 1905 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, June 8.— "The Elastic Properties of Steel 

 at High Temperatures." By Prof. B. Hopkinson and 

 F. Rogers. Communicated by Prof. Ewing, F.R.S. 



In the experiments described in this paper, the elastic 

 properties of steel and iron have been investigated at 

 higher temperatures, ranging up to Soo° C, and for 

 stresses greatly below that required to rupture the material. 

 The authors have found that as the temperature rises the 

 stress-strain relations undergo a remarkable change, which 

 may best be expressed by saying that what is variously 

 called the " time-effect," or " elastische nachwirkung," 

 or " creeping," increases greatly with the temperature. 

 Steel, at high temperatures, behaves like indiarubber or 

 glass ; if it is stressed for a time, and the stress removed, 

 it does not at once recover, but after the immediate elastic 

 recovery there is a slow contraction perceptible for many 

 minutes. Such " creeping " can be detected at the ordinary 

 temperature, but at a red heat it attains a different order 

 of magnitude, becoming (in its total amount) a substantial 

 fraction of the whole deformation. 



This phenomenon is analogous to residual charge in 

 glass and other dielectrics ; the stress corresponding to the 

 electric force, and the strain to the electric displacement. 

 Whether the law of linear superposition of the effects of 

 stresses — closely followed in the electrical analogy — is true 

 for hot steel or iron, is an interesting question which the 

 apparatus used was hardly sufficiently delicate to answer. 



The magnitude of this effect in steel may best be gauged 

 by comparing it with other cases of the same kind, e.g. 

 with the slow recovery of a glass fibre after twisting ; if 

 such a fibre be twisted through a considerable angle for 

 several hours, it will recover all but one-fiftieth of the 

 twist within two or three seconds of the removal of the 

 stress. The remaining slow "creep," amounting to one- 

 fiftieth of the whole deformation, corresponds to the slow 

 return of the steel. In indiarubber, in certain circum- 

 stances, 10 per cent, of the strain disappears in time after 

 the removal of the stress. But in steel, at 600° C, the 

 proportion is about 15 per cent. 



.'\nother effect of " creeping," such as the authors have 

 observed, is to make the determination of Young's modulus 

 a matter of some uncertainty. Thus the extension of the 

 bar at 600° C. produced by a given load varies 15 per cent, 

 or more, according to the time of application of the load. 

 When, however, the load is applied for a very short time, 

 say of the order of one or two seconds, the strain produced 

 seems to approach to a definite limiting value which is 

 the instantaneous extension or contraction of the bar 

 observed in the experiments when the load is applied or 

 removed. It seems reasonable to define Young's modulus 

 for a metal in this state, as the stress divided by this 

 limiting instantaneous strain. It is then independent of 

 the manner of loading, and is a definite physical constant ; 

 otherwise not. 



"On the Refractive Index of Gaseous Fluorine." By 

 C. Cuthbertson and E. B. R. Prideaux. Communicated 

 by Sir William Ramsay, K.C.B., F.R.S. 



The authors have determined the refractive inde.x of 

 gaseous fluorine for sodium light by means of Jamin's 

 refractometer. Five experiments gave values for the 

 refractivlty (fi—i) 10" of 195, 177, 192, 194, and 198^. The 

 discrepancy exhibited by the second experiment can be 

 iiccounted for, and it is believed that the mean of the 

 other four exneriments, 195, is within 2 or 3 per cent, 

 of (he true value. 



In a recent paper (Phil. Trans., A, vol. cciv. p. 323), one 

 of the authors has attempted to show that the refractivities 

 of the different members of the same chemical group are 

 related in the ratios of small integers ; and it was observed 

 that, if this coincidence were not due to chance, the re- 

 fractivlty of fluorine should bear to that of chlorine the 

 ratio of i to 4, which those of neon, oxygen, and nitrogen 

 bear to argon, sulphur, and phosphorus respectively. This 

 prediction has been verified. The refractivlty of chlorine 

 for sodium light is 768, or 192x4; and that now found 

 for 'fluorine is 195, a discrepancy of lA per cent., which is 

 well within the limits of error of the experiment. 



NO. 1 87 I, VOL. 72] 



CONTENTS. 



P.\GE 



Marine Engineering 453 



The Birds of Iceland. By R. L 454 



Our Book Shelf;— 



Fiitsch and Bayer: " Neue Fische und Replilien aus 



der biihrnipchen Kreideformation." — A. S. W. . . 454 

 Wehner : " Die Bedeutung des Experimentes fiir den 



Unterricht in der Chemie." — A. S 455 



Kieffer : " Monographic des Cynipides d'Europe et 



d'Algerie."— W. F. K 455 



Richards: " The Gum Bichromate Process " .... 455 

 Letters to the Editor : — 



Recent Changes in Vesuvius. {Illustraled.) — R. T. 



Giinther 455 



The Millport Marine Station.— S. Pace 456 



The Total Solar Eclipse, August 30. (flhis/raleiJ.) 



(1) The Solar Physics Cibseivaloty Expedition. By 



Dr. William J. S. Lockyer 457 



(2) Reports of Observations 45^ 



Technical Education in Natal 460 



The Woburn Experimental Fruit Farm. By Prof. 



T. H. Middleton 461 



Notes. (IHiislrali'd.) 461 



Our Astronomical Column : — 



Discovery of a Nova, ill/nslrated.) 465 



Water Vapour in the Martian Atmosphere 465 



Real Paths of Lyrid Meteors 4^5 



Observations of Satellites 465 



The British Association ; — 



Section (.;. — lingineering — Opening Address by 



Colonel Sir C. Scott Moncfieff, K.C.S.I., 



K.C.M.G., R.E , LL.D.. President of the Section 465 



Section II. — Anthropolotjy. — Opening Address by 



A. C. Haddon, Sc.D/; F.R.S., President of the 



Section 471 



University and Educational Intelligence 



(Ilbiiti-alcd) 479 



Societies and Academies 4S0 



P.ARIS. 



Academy of Sciences, August 28. — M. Troost in the 

 chair. — The ultra-violet spectra of the reversing layer 

 during the total eclipse of May 28, 1900 : H. Deslandres. 

 An account of the apparatus employed, and a short list 

 of the principal lines of titanium, vanadium, and 

 chromium observed. — On a differential equation of the 

 fourth order : Gaston Darboux. — On transcendental 

 numbers : Ed, Maillet. — Researches on irradiation : 1 

 .\drien Guebhard. — On a method suitable for the study i 

 of a luminous phenomenon varying in intensity with the 

 time. .Application to the determination of the instan- 

 taneous velocity of a rotating mirror and to the study of 

 the Hertzian spark : .\. Turpain. The arrangement is 

 a modification of the Foucault experiment for the deter- 

 mination of the velocity of light. The receiving eye-piece 

 is replaced by a photographic plate, and the spark is 

 placed between the rotating and fixed mirrors. The 

 measurement of the distance on the negative between the 

 two images, the one caused by the light travelling directly 

 and the other by reflection from the fixed mirror, and of the 

 distances apart of the portions of the apparatus, gives an 

 accurate determination of the velocity of the mirror, the 

 velocity of light being taken as known. The method has 

 been also applied to the study of the spark given by a 

 Hertzian exciter and resonator, but the description of this 

 part of the work is reserved for a later communication. 

 — A new group of protophytic parasites, Eccrinides : L. 

 Legrer and O. Duboscq. — A contribution to the cyto- 

 logical study of the Cyanophycese : A. Guilliermond. — 

 .^terigmalocystis nigra and oxalic acid : P. G. 

 Charpentier. This mould, when cultivated in Raulin's 

 fluid, never secretes oxalic acid before .spore formation 

 takes place, but sporulation acts only indirectly in causing 

 the secretion, this being caused by the exhaustion of the 

 medium. 



