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NATURE 



\_March 4, 1880 



thermometer with a reservoir of iron or glass inclosed by 

 a non-conducting material. In the sides of the reservoir 

 tubes of glass or platinum are introduced, extending deep 

 into the mass of mercury. In these tubes the reactions 

 between weighed amounts of various substances take 

 place, and the heat given off to the surrounding mass of 

 mercury causes a corresponding rise in the thermometer 

 tube. The second apparatus devised for measuring the 

 heat ensuing from the combustion of gases, is much more 

 complicated, being modelled after Dulong's classical 

 calorimeter, but altered in a variety of ways so as to 

 ensure the utmost accuracy in the results. It is to these 

 instruments, or modifications of the same, that we owe a 

 large proportion of the data serving as a basis for our 

 present knowledge of thermo-chemistry. Among the 

 long series of observations carried out by their means, 

 the most important were the series of experiments on com- 

 bustions in oxygen gas ; on the action of gases on each 

 other, and on liquid or solid bodies ; on the influence of 

 dimorphism on the heat evolved by combustion, as in 

 the case of red and vitreous phosphorus, where there is a 

 difference of 16 per cent, in the number of units of heat 

 resulting from oxidation ; on the influence of polymerism, 

 in which it was shown that the amount of heat evolved 

 decreases with the increase of density in the vapour 

 resulting from combination with oxygen ; on the pro- 

 perty of metameric bodies to yield different degrees of 

 heat ; on the relative diminution in the heat evolved by 

 the combustion of a compound body, compared with that 

 due to the combustion of its various constituents ; on the 

 combination of bases with acids, in which it was shown 

 that the amount of heat evolved by the union of equiva- 

 lent quantities of different acids with a given base is 

 nearly always the same ; on the heat evolved by metallic 

 precipitations ; on the heat developed by the solution of 

 salts and gases ; on the heat evolved by the absorption 

 of gases in porous bodies, especially in connection with 

 the condensation of hydrogen by means of palladium or 

 platinum ; on the phenomena of heat resulting from the 

 mixture of liquids ; on the development of heat in con- 

 nection with the compression of liquids ; on the specific 

 and latent heat of a number of bodies ; on the heat 

 developed by the electrolysis of various compounds, and 

 on the development of heat in electric conductors, and in 

 electric action generally. Closely allied to some of the 

 above researches were studies on the changes in volume 

 consequent upon solution ; on the dissociation of crystals ; 

 on the chemical effect of light ; on electrolysis ; and on 

 the influence of pressure on solubility, in which connec- 

 tion he ascertained that the solubility of certain salts was 

 increased when submitted to a pressure of from thirty to 

 sixty atmospheres. Of the labour attendant upon the 

 observation and recording of so extensive a series of 

 experiments, it is difficult to form an adequate ilea. As 

 a monument of the patient, painstaking, conscientious 

 collation of valuable physical constants, they rank 

 among the achievements of modern physical chemistry, 

 while too much praise cannot be accorded to the address 

 and ingenuity with which the mechanical difficulties of so 

 wide and varied a range of experiment were successfully 

 met and overcome. 



The results obtained by Favre alone or in connection 

 with Silbermann, united with those due to the classical 

 contemporaneous researches of Andrews, form practically 

 the basis of modern thermochemistry, the introduction of 

 their methods of exact measurement having much the 

 same influence as Lavoisier's introduction of the chemical 

 balance. Under the impetus given by their investiga- 

 tions, Berthelot in Paris, and especiallv Thomsen in 

 Copenhagen, have during the last decade rapidly per- 

 fected and elaborated this subject, until at the present 

 day there are few branches of chemical physics based on 

 so numerous and varied experimental data. 



The labours of Prof. Favre were recognised in France 



by his nomination to the Legion of Honour, and by his 

 election as a Corresponding Member of the Academy of 

 Sciences in the Section of Chemistry. 



ARAGO 

 \X/"E recently gave some account of the inauguration 

 * * of a statue to Arago at Perpignan. We now give 

 an illustration of that statue, with some extracts from the in- 

 teresting address delivered by Dr. Janssen, who was present 

 at the ceremony as representative of the Paris Academy 

 of Sciences. After speaking of Arago' s visit to Spain, 

 and his election as a member of the Academy, Dr. 

 Janssen went on to say : — 



The young physicist was not long in surpassing the 

 hopes which they (the Academicians) had placed in him. 

 Within two years of his election he had laid before the 

 Academy many very important memoirs, and a noble 

 discovery which gave birth to a beautiful chapter of 

 optics, the discovery of chromatic polarisation, as it is 

 now called. He observed that polarised light acquired 

 certain entirely new properties when made to pass through 

 properly prepared crystalline plates. The brilliant 

 phenomena of colours to which polarised light could 

 give birth in these circumstances had a great theoretical 

 bearing, and in the hands of Arago they became the bases ot 

 the most ingenious and important applications, the principle 

 one being the invention of a polariscope which disclosed 

 the least traces of polarised light, and which Arago was 

 able to employ in determining the gaseous nature of the 

 sun's dazzling surface. 



Gentlemen, it was a great and glorious epoch for our 

 Academy. The discoveries regarding light and the 

 principles which regulated its phenomena succeeded each 

 other almost regularly. Malus, Arago, and Fresnel were 

 at the head of this great scientific movement in France. 

 After Malus, who in 1808 discovered polarisation by 

 reflexion, and a little later assigned its laws, Arago pub- 

 lished this series of his beautiful works on chromatic 

 polarisation, on circular polarisation, and the photometer; 

 he adduced in favour of the wave theory the capital fact of 

 the retarding influence of a thin metal plate in this system 

 of two interfering rays of light. Finally Fresnel appeared 

 on the scene, and this genius, so simple, yet so profound, 

 connected these discoveries without an effort, and attached 

 them again to the principle of undulations, of which he 

 showed the fruitfulness, and which in his hands received 

 its final definite triumph. Arago then has taken his 

 place in this aristocracy, but posterity owes to him a 

 still greater obligation. Thanks to his perspicacity in 

 divining merit, thanks to the natural generosity of his 

 disposition, exempt as it was from all jealousy, Fresnel, an 

 obscure provincial engineer, was found out, encouraged, 

 and called to Paris, where he had a situation. Arago 

 formed a friendship for him which was never dimmed by 

 a cloud and he missed no opportunity of supporting his 

 works and the interests of his fame. Between such 

 rivals in glory, a sentiment so pure and noble is one of 

 the finest spectacles which the human mind can offer us. 

 Truly, gentlemen, posterity should delight to allow a moral 

 share to Arago in the grand scientific monument which 

 it has received from the genius of Fresnel. 



" The movement which produced these remarkable 

 discoveries in light began to slacken when there came to 

 us from Denmark in 1820, the announcement of a 

 scientific fact of a very different character but of immense 

 importance, and which threw back on electricity almost 

 all the activity of the scientific world. Every one knows 

 (Ersted and the discovery of the action of the current 

 on the magnetised needle. The relations which ought to 

 unite magnetism and electricity had long been foreseen, 

 but the common bond had always eluded those who 

 attempted to seize it. Now the bridge was thrown, and 



