420 



NATURE 



{March 4, 1880 



career at the Observatory has left memories which are 

 still living among us. Wherever Arago was to read or 

 speak there was eagerness to hear him, and this eagerness 

 was manifested by all classes and by men in all stages 

 of education, from the scholar who was charmed to see 

 with whit art the master could, in treating a difficult 

 subject, seize the side which would render it intelligible to 

 all, to the artisan astonished at being able to understand 

 and to receive clear, precise ideas on matters which he 

 believed for him to be absolutely inaccessible. The cause 

 of this success, gentlemen, lay in the harmony of mental 

 and physical gifts, which I attempted to characterise at 

 the beginning of this speech. They lay above all in that 

 superior comprelvnsion of subjects which he had deve- 

 loped by his labours and discoveries. He who has 

 created in science, teaches very differently from the most 

 educated professor who has never stirred the bowels of a 

 subject in order to get at fresh truths. There are three 

 degrees in the knowledge of truth ; namely, those of 

 student, teacher, and discoverer. In order to practise in 

 a superior manner in one of these degrees, it is necessary 

 to be raised to a stage which dominates it. As has been 

 truly said, one does not thoroughly understand that which 

 one is unable to teach. I say even that inventors alone 

 can teach in a transcendent manner. That is not to say 

 that all inventors are popular teachers. There are men of 

 genius who like to hold themselves aloof, and whom it 

 is to keep from others the truths of which they 

 sed themselves without effort ; there are others, who 

 although rich in the faculties of invention, have none of 

 which make the professor. But when all these gifts 

 are united, and when to a zealous spirit are added the 

 faculties of a superior mind, then we have one oi 



popular teachers whose action extends over a whole 

 1. Such was Arago, and such the real character of 

 tness. 



irago's writings shall not only have been 

 of service to the generation which enjoyed them so ea 

 We inherit them and we shall not be tl >sterity. 



Among them, indeed, how many chefs-d'awvre will always 

 be consulted, in spite of the advance of science, on 

 unt of the perfection of their form and theii 

 ■ : c u 1 ideas. 



(jcech would be incomplete if we did not add 

 some touches to the grand and sympathetic figure. 



I, has not only served science by his discoverie 

 urs, his writings, and his teaching; he his served it 

 by the protection and the encouragement which he 

 1 to lavish on the young philosophers of the future, 

 on inventors of merit, and on all those who called upon 

 him with any title. Jus'- now I cited the case of J 

 but twt nty other examples, many of them illustrious, could 

 be invoked. 



survey our Comptes Ranhiswz shall sec the name 



of Arago constantly intervening, whether he deals with 



an important discovery, a meritorious work, or a rcmark- 



[f the affirmations which he makes, or 



praises which he believes to be merited encounter 



isition, his speech then takes fire, he becomes excited 



and indignant, and overturns all obstacles. How many 



have had him as their all powerful advocate, who have 



subsequently forgotten i: ? 



1 Arago had to deliver a speech at the Academy 

 on an important subject, it was quite an event. V* e 

 know by tradition, for example, the impression caused at 

 the sitting when Arago expounded the discovery ol 

 Daguerre, and the interest, the pleasure, the admiration 

 which was produced in the hall on hearing this master of 

 the mysteries of light, revealing the operations which 

 allowed of the fixing of the figure in the camera-obscura. 

 Among so many applications which his perspicacity fore- 

 for the admirable discovery, he was always struck by 

 those which concerned astronomy. 



Faye, one of Arago's students and our eminent co- 



worker, has sustained this idea and has signalised by 

 many claims all the ways which can be devised for 

 the application of photography to celestial phenomena. 



Let us also recall the sittings when Arago explained 

 the success of Crenelle's operations in the boring of wells, 

 with which he was desirous of endowing the capital, and 

 which we owe to his sagacity and to the perseverance by 

 which he was able to triumph over general incredulity. 



Finally among so many fruitful initiatives, let us remark 

 in particular that which Arago took with regard to Meat's 

 pension. Arago proposed that a national pension should 

 be given to the great engineer, to whom France owed so 

 many fine works. There was only one almost forgotten 

 precedent. Arago wished to create a brilliant one. This 

 great spirit felt how much the institution of national 

 pensions accorded to those who had wrought gloriously 

 for the benefit of the country, and who in the struggle 

 have forgotten themselves, would produce devotedness to 

 the country. Let us apply generally, gentlemen, the 

 example which is offered to us under the patronage of 

 Arago. Let us give to the men, never very numerous, 

 who e conspicuous services have received the recognition 

 of the country, that proof of its justice. Then, even, 

 though the recompense be materially modest, there will 

 always be attached to it a special value, it will always 

 excite the noblest emulation, because each reward that is 

 thus offered in the name of the country becomes a 

 medal. 



Gentlemen, in the decline of his career, this great 

 soul had worn out the body on which it had made such 

 severe demands. His organs were no longer able to serve 

 that powerful intelligence in realizing his scientific con- 

 ceptions. Arago then gave a last proof of his generosity. 

 Having conceived the project of a magnificent experiment 

 on light, he went to the Academy, expounded his ideas, 

 and invited the young philosophers to follow them out 

 and to gather the glory of their realization. Thus it was 

 that Foucault and Fizeau, aided by our eminent artist and 

 colleague Breguet, were brought to the works by which 

 they have begun their great scientific reputation. 



Shortly after, Arago, broken by disease, and feeling 

 his end near, wished to bid a last farewell to that Academy 

 which had held so great a place in his life, of which he 

 was the organ for so many years, and where his voice, 

 listened to, loved, and admired, had resounded for almost 

 half a century. His death, on October 2, 1853, was a loss 

 to the whole world. 



VESBIUM 



PROF. A. SCACCHI, who has been for some time 

 engaged in chemical investigations on the 

 which issued from Vesuvius during the year 1631, has 

 recently made an interesting communication to the Royal 

 Academy of Sciences at Naples with regard to the 

 probable presence in these deposits of a new metal. The 

 material which Prof. Scacchi has operated upon consists 

 of delicate yellow incrustations found in the crevices of the 

 lava, in company with atacamite and azzumite, and has 

 been named by him vesbine, while the supposed new 

 metal is termed ves Mum. Both words arc derived from 

 the ancient: name for Vesuvius mentiored by Galen in his 

 work, "De Morbis Curandis" (Book v. Chap. 12). Yes- 

 bine is found to consist of silicates of copper, the alkalies, 

 iron, aluminium, e\;c., together with small quantities ol 

 the salts of what receives the name vesbic acid. The 

 latter is obtained in an impure state— containing traces of 

 iron, aluminium, lead, and copper— by evaporating the 

 solution of vesbine in hydrochloric acid to 170 C, ex- 

 tracting with water, treating the residue of silicic acid, 

 and vesbiates with hydrochloric acid, filtering from silicic 

 acid, evaporating again to 170 , and extracting with water. 

 The dark green residue thus obtained formed the materia! 

 for the scries of investigations on which the discoverer 



