54^ 



NATURE 



{Oct. 2, 1879 



introducing them into a hydrogen flame, was dne to the rapid 

 disintegration of the metal. I have ascertained the cause of 

 this phenomenon, and have succeeded in eliminating that which 

 produces it, and in doing so have produced a metal in a state 

 hitherto unknown, and which is absolutely stable at a tempera- 

 ture where nearly all substances melt or are consumed ; a metal 

 which, although originally soft and pliable, becomes as homo- 

 geneous as glass and as rigid as steel. When wound in the form 

 of a spiral it is as springy and elastic when at the most dazzling 

 incandescence as when cold, and cannot be annealed by any 

 process now commonly known, for the cause of this shrinking 

 and cracking of the wire is due entirely to the expansion of the 

 air in the mechanical and physical pores of the platinum, and 

 the contraction upon the escape of the air. rhtinum as sold in 

 commerce may be compared to sandstone, in which the whole is 

 made of a great number of particles with many airspaces. The 

 sandstone upon melting becomes homogeneous and no air spaces 

 exist. 



With platinum or any metal the air spaces may be eliminated 

 and the metal made homogeneous by a very simple process. This 

 process I will now describe. I had made a large number of 

 platinum spirals, all of the same size and from the same quality 

 of wire ; each spiral presented to the air a radiating surface of 

 three-sixteenths of an inch ; five of these were brought by the 

 electric current up to the melting-point, the light was measured 

 by a photometer, and the average light was equal to four standard 

 candles for each spiral just at the melting-point. One of the 

 same kind of spirals was placed in the receiver of an air-pump, 

 and the air exhausted to 2 millimetres ; a weak current was then 

 passed through the wire, to slightly warm it for the purpose of 

 assisting the passage of the air from the pores of the metal into 

 the vacuum. The temperature of the wire was gradually 

 augmented, at intervals of ten minutes, until it became red. 

 The object of slowly increasing the temperature was to allow the 

 air to pass out gradually and not explosively. Afterward the 

 current was increased at intervals of fifteen minutes. Before 

 each increase in the current the wire was allowed to cool, and the 

 contraction and expansion at these high temperatures caused the 

 wire to weld together at the points previously containing air. In 

 one hour and forty minutes this spiral had reached such a tem- 

 perature without melting that it was giving a light of twenty- 

 five standard candles, whereas it would undoubtedly have melted 

 before it gave a light of five candles had it not been put through 

 the above process. Several more spirals were afterwards tried, 

 with the same result. One spiral, which had been brought to 

 these high temperatures more slowly, gave a light equal to thirty 

 standard candles. In the open air this spiral gave nearly the 

 .'•ame light, although it required more current to keep it at the 

 same temperature. Upon examination of these spirals, which 

 had passed through the vacuum process, by the aid of a micro- 

 scope no cracks were visible ; the wire had become as white as 

 silver, and had a polish which could not be given it by any other 

 means. The wire had a less diameter than before treatment, 

 and it was exceedingly difficult to melt in the oxy-hydrogen flame. 

 As compared with untreated platinum, it was found that it was 

 as hard as the steel wire used in pianos, and that it could not be 

 annealed at any temperature. 



My experiments with many metals treated by this process 

 h«ve proved to my satisfaction, and I have no hesitation in stating 

 that what is known as annealing of metals to make them soft and 

 pliable is nothing more than the cracking of the metal. In every 

 case where a hard drawn wire had been annealed a powerful 

 microscope revealed m)Tiads of cracks in the metal Since the 

 experiments of which I have just spoken I have, by the aid of 

 Sprengel mercury pumps, produced higher exhaustion, and have, 

 by consuming five hours in excluding the air from the wire and 

 intermitting the current a great number of times, succeeded in ob- 

 taining a light of eight standard candles from a spiral of wire 

 with a total radiating surface of I -32nd of an inch, or a surface 

 about equal to one grain of buckwheat. With spirals of this small 

 size which have not passed through the process, theaverage amount 

 of light given out before melting is less than one standard candle. 

 Thus I am enabled, by the increased capacity of platinum, to with- 

 stand high temperatures, to employ small radiating siu-faces, and 

 and thus reduce the energy required for candle light. I can now 

 obtain eight separate jets, each giving out an absolutely steady 

 light, and each equal to sixteen standard candles, or a total of 

 128 candles, by the expenditure of 30,000 foot-pounds of energy, 

 or less than one horse-power. As a matter of curiosity I have 

 made spirals of other metals, and exckded the air from them 



in the manner stated. Common iron wire may be made to give 

 a light greater than platinum not heated. The iron becomes as 

 hard as steel, and just as elastic. Nickel is far more refractory 

 than iron. Steel wire used in pianos becomes decarbonised, but 

 remains hard, and becomes the colour of silver. Aluminium 

 melts only at a white-heat. 



In conclusion, it may be interesting to state that the melting- 

 points of many oxides is dependent on the manner of applying 

 the heat ; for instance, pure oxide of zirconium does not fuse in 

 the flame of the oxy hydrogen blow-pipe, while it melts like wa:t 

 and conducts electricity when on an incandescent platinum spiral 

 which is at a far lower temperature ; on the other hand oxide of 

 aluminum easily melts in the oxy-hydrogen flame, while it only 

 vitrifies on the platinum spiral. 



THE INAUGURATION OF ARAGO'S STATUE 



'T*HE statue to Arago recently unveiled at Perpignan is not the 

 first erected to that great astronomer and greater physicist. 

 In 1867 M. Isaac Pereire, then representative of the native place 

 of Arago in the Imperial Chamber of Deputies, erected one at 

 his own expense at Estagel. The inauguration was accompanied 

 by speeches delivered by the generous donor, M. Bertrand, the 

 perpetual secretary of the Academy of Science, and others. It 

 was stated then that Arago had supported against his own 

 party the construction of the railways by public companies, and 

 had been grossly abused by some of his political frienrls. 

 Although a political leader, it must be said, to the glory of 

 Arago, that he never was influenced by party considerations. 

 He was always writing, and speaking, and voting according to 

 the dictamina of his own judgment. These facts should be 

 remembered, as efforts have been made in the recent Arago 

 celebration, to degrade him into a mere politician, which never 

 was the case. Arago was made a member of the Provisional 

 Government of France in February, 1848 ; it was owing to his 

 personal exertion that the abolition decree was proclaimed before 

 the convocation of the National Assembly. It is true that he 

 was appointed in the beginning of May one of the quinqutmvirs 

 of the Executive Commission. But this Government was over- 

 thrown by the popular rising of the end of June, and from 

 that time he abstained from taking any prominent part in 

 politics. 



Arago was not rich, his works having been mostly published 

 in the Annuain du Bureau des Longitudes without any copyright, 

 and sold for the benefit of the Bureau, of which he was the most 

 influential member. His paying works were all of them posthu- 

 mous, and edited by M. Barras, the Perpetual Secretary of the 

 Agricultural Society of France. The sale was not so large a» 

 anticipated, and the publisher who purchased the copyright from 

 the inheritors failed. The sale of the Annuaire was so large 

 during Arago's lifetime, that the Bureau had a profit by it. 

 Since his death it has become necessary to provide special funds 

 for the publication of that useful work. 



Arago had no salary at all as director of the Observatory. He 

 was appointed every year by the Bureau, receiving only 200/. 

 for his membership. His other salaries were 50/. as a member 

 of the Academy of Sciences, 250/. as Perpetual Secretary, and 

 when he was lecturing on astronomy 50/. The functions of 

 deputy and member of Municipal Council of Paris being entirely 

 gratuitous, he was no receiver of any other public moneys. 

 Under the Republic his membership of the Assembly brought 

 him l/. a day. 



From the eloquent iloge pronounced by M. Paul Bert at the 

 recent inauguration, we take the following extract : — 



" To contemplate Arago under all the aspects that may attract 

 the admiration of posterity we must think of him as a man of 

 science overturning the Newtonian hypothesis of the emission of 

 light, determining the physical constitution of the sun, explain- 

 ing the scintillation of the stars, the nature of the aurora borealis, 

 discovering magnetisation by currents, the origin of the electric 

 telegraph, extending to all bodies magnetic properties ; finally, 

 for I must limit myself to the most prominent points, indicating 

 to the most eminent of his disciples the star still unkno%vn and 

 invisible, whose discovery introduced order among the per- 

 turbed planets, and which still remains the most extraordinary 

 mark of the power of human genius. As a professor, 

 again, before three thousand auditors at the Observatory, or 

 in his chair as Perpetual Secretary writing his incomparable 

 scientific notices, or dictating, when blind, his popular astronomy, 

 always, by speech or by pen, marvellous for his clearness, lis. 



