40^ 



NATURE 



[June 19, 1913 



support of his view. Unfortunately, as Prof. Arnold 

 has pointed out, the heating curves" actuallv show the 

 Ac2 change. It is true that they are less strongly 

 marked than the Ara changes, but this is only what 

 would be expected. 



The changes during heating, as shown by inverse 

 rate curves, extend over a greater range and are 

 therefore less strongly marked than in the cooling 

 curves. This is well shown in the A3 change shown 

 in the curves, and in view of the fact that the Ar2 

 change is itself very small, it was scarcely to be ex- 

 pected that the Ac2 change would be very easily 

 detected. Moreover, Prof. Carpenter has shown that 

 if the iron, after cooling just below Ar3, is held at 

 that temperature for two and a half hours in order 

 to allow the change from 7 to a iron to become com- 

 plete, and then slowly cooled, the Ar2 change is shown 

 as decidedly as before. He attempts to explain this 

 by assuming that the impurities present are sufficient 

 to prevent actual contact of the 7 and a molecules, but 

 the explanation is unsatisfactory, and his results must 

 be regarded rather as proving than disproving the 

 independence of the A2 critical point. 



The paper by Dr. Rosenhain and Mr. Humfrey 

 describes a series of experiments admirably conducted 

 with the aid of an ingeniously constructed testing 

 machine, in order to investigate the physical proper- 

 ties of mild steel at high temperatures. It is impos- 

 sible to describe the experiments in detail, but the 

 results show that the curve representing the tenacity 

 at high temperatures consists of three branches corre- 

 sponding to the 7, /3, and a ranges of iron. Starting 

 at 1100 C, the tenacity increases as the temperature 

 falls, until the Ar3 point is reached, when there is a 

 rapid decrease in tenacity. This is followed by a 

 further increase until Ar2 is reached, when there is 

 another falling off in tenacity. The influence of the 

 rate of strain is discussed, also the influence of vary- 

 ing size of crystals; and photographs are given to 

 illustrate the types of fracture at different tempera- 

 tures. The authors conclude that they find it difficult 

 to reconcile their results with Benedicks's theory by 

 which j3 iron is regarded as a solution of 7 iron and 

 a iron. 



Prof. Arnold's contribution to the discussion when 

 separated from side issues resolves itself into little 

 more than a reassertion of his own theories, which he 

 claims are supported by the two papers in question. 

 The one useful criticism which Prof. Arnold makes 

 has already been referred to, in which he points out 

 that the Ac2 change is observable in Prof. Carpenter's 

 curves. 



The criticism of Dr. Rosenhain and Mr. Humfrev's 

 paper is even less helpful. It is claimed that the 

 authors' conclusions are of no value owing to their 

 "erroneously presupposing" that they are discussing 

 results obtained from chemically pure iron rather than 

 from their dead mild commercial steel." It is possible 

 that the authors have underestimated the importance 

 of the impurities in their steel and have pushed their 

 conclusions a little too far, but they give full details 

 of the material upon which their experiments have 

 been carried out. and they make no claim that their 

 conclusions are final. Nevertheless, the authors have 

 laid themselves open to some criticism inasmuch as 

 they have chosen for their experiments a steel which, 

 even from a commercial point of view, is of verv 

 poor quality. 



As a matter of fact, the importance of the discus- 

 sion has been exaggerated, and the two naoers leave 

 the & iron theory very much where it was before. The 

 somewhat ill-defined A2 change and its relation to 

 the physical properties of steel will still attract the 

 attention of men of science who are anxious to dis- 

 NO. 2277, VOL. 91] 



cover the truth. Other papers will be read and 

 further discussions will take place, but in the mean- 

 time, and until further evidence is forthcoming, those 

 who are wise will refrain from a too dogmatic insist- 

 ence upon their own particular views. 



THE ROYAL SOCIETY CONVERSAZIONE. 



'"THE annual June conversazione of the Royal Society 



*■ was held in the rooms of the society at Burlington 

 House on June 11. As is usual upon such an occasion, 

 I various instruments and objects of scientific interest 

 were exhibited. Most of these have been described 

 already in the account of the May conversazione given 

 in Nature of May 15 Ip. 273). Other exhibits are 

 mentioned below : — 



Dr. E. C. Pickering : Colour-blindness, if anv_, of 

 eminent astronomers. The sensitiveness of the eve 

 to rays of different colours has been tested for nume- 

 rous astronomers by grouping their estimates of the 

 light of the stars according to their colour, as shown 

 by the class of spectrum. The earliest estimates, 

 those of Ptolemy and Sufi, show results agreeing 

 closely with those of recent times. Peirce shows a 

 marked sensitiveness to the red, and Seidel to the 

 blue, rays. The latter effect is still more marked in 

 photographic plates. 



Prof. Silvanus P. Thompson: Poulsen's telegraphon. 

 The telegraphon of Dr. V. Poulsen, of Copenhagen, 

 is an apparatus which records speech or sound trans- 

 mitted by telephone, and reproduces it, at any subse- 

 quent time, in another telephone. The recording is 

 effected magnetically. In this newest pattern, a thin 

 wire of tungsten steel is caused to run rapidly between 

 the poles of a small electromagnet in the receiving 

 circuit of the telephone ; and this electromagnet im- 

 presses the corresponding vibrations on the wire bv 

 magnetising it in an immense series of minute local 

 spots. The record on the wire is absolutely invisible. 

 On passing the wire again between the poles of a 

 small electromagnet in the circuit of a receiving tele- 

 phone, the series of minute magnetic spots on the 

 wire sets up, by magneto-electric induction, a corre- 

 sponding series of electric undulations, causing the 

 telephone to emit a corresponding sound. The sounds 

 so reproduced are faint unless a Brown telephone 

 relay is employed to magnify them. 



Mr. R. Inwards: Spiraloid curve apparatus. This 

 is an instrument consisting of a revolving table carry- 

 ing the paper, and over which a pen is caused by 

 gear-wheels and adjustable cranks to describe an un- 

 dulating line, and to produce figures resembling the 

 structure of the Diatomacese, Radiolaria, and other 

 natural forms. 



Mr. C. R. Darling: Experiments with liquid drops 

 and skins. (1) Large drops of liquids may be formed 

 in media of slightly less density, e.g. orthotoluidine 

 in water at 18 C. The formation is gradual, and all 

 the stages may be observed by the unaided eye. If 

 two drops of different diameters be made to com- 

 municate through a tube, the lesser passes into the 

 greater when both are at the same level ; if, however, 

 the lesser drop be lowered, the movement is reversed. 

 A position of equilibrium may be found in which both 

 drops are stationary. (2) Skins of aniline may be 

 formed on suitable frames under water, and made 

 into bubbles filled with water. (3) Skins of various 

 liquids on the surface of water exhibit characteristic 

 movements, depending upon the liquid used. 



Dr. T. K. Rose : Recrvstallisation of gold on anneal- 

 ing. The specimens exhibited of incompletely annealed 

 gold show that the new crystals make their appear- 

 ance singly when annealing begins, and that as the 

 temperature is raised or the time prolonged, othrr 



