224 



NA TURE 



[July 6, 1893 



said M. Tisserand, " and gave it a permanent place. Be- 

 fore him, astronomers concerned themselves chiefly with 

 the movements of stars and members of our planetary 

 system, seeking to explain them in their minutest details 

 by the law of gravitation. Arago studied the nature of 

 heavenly bodies, and the character of the phen imena 

 continually exhibited by them. The polariscope showed 

 him that the glaring surface of the sun is gaseous, and 

 gave him important information as to the light of comets. 

 Another application of physical methods furnished him 

 with a precise means for measuring the 

 diameters of planets or determining their 

 magnitude. Nothing is more ingenious than 

 his explanation of the scintillation of stars, 

 founded upon the remarkable properties 

 Fresnel found to be possessed by rays of 

 light. Arago ought truly to be considered as 

 the founder of a branch of astronomy — physical 

 astronomy — that has since been remarkably 

 extended, for it was he who pointed out the 

 importance that would accrue from the appli- 

 cation of photography to the study of celestial 

 bodies. He was not able to foresee the day, 

 however, when chemistry would enter into the 

 domain of astronomy, and we should be able 

 to discover their constitution ; spectrum analysis 

 has only been discovered, in fact, since the 

 death of Arago." 



" An example will give an idea of the per- 

 spicacity of Arago. It is generally known that 

 about the end of last century France took the 

 initiative of the metrical system and made it an 

 international thing by connecting the metre 

 with the size of the earth. But our globe is 

 cooling and contracts, little by little, in the 

 course of centuries, so that the unit of length 

 is rendered liable to slight changes. Arago 

 thought that a minute study of the light-rays 

 that come to us from the sun and stars might 

 furnish a rigorously constant unit of length, 

 connected not with the earth, but with the stars 

 — a sidereal metre of some kind. Well, this 

 beautiful idea was realised a few months ago 

 by Mr. Michelson, at the American Bureau 

 of Weights and Measures." M. Tisserand also 

 dwelt upon the influence that Arago exercised 

 upon his pupils and the comprehensive character 

 of his literary works. M. Cornu followed with 

 an account of Arago's investigations in experi- 

 mental physics, and after stating his work in 

 connection with the experimentum cruets of 

 the emission and wave theories of light, said, 

 " If we come to terrestrial physics, meteorology, 

 or industrial applications of steam and elec- 

 tricity, we always find Arago in the front rank 

 with new ideas. Of an indefatigable activity, 

 in science as in government, he was present 

 with all the resources of his powerful spirit, with 

 ilie ardour of his generous heart, especially 

 where there was a great work to direct, a just 

 c tuse to defend, a social evil to fight, and, at 

 the call of duty, a peril to face." 



The character of the statue, which is in bronze, is 

 shown in the accompanying illustration from La Nature. 

 Arago has his face turned towards the observatory. 

 The pedestal on which the figure stands is also in 

 bronze, and bears the simple inscription "Francois 

 Arago, 1786-1853, Souscription Nationai.e." ivien 

 of science throughout the world respect the name, 

 and their French confreres revere it. Those who have 

 done homage to the man by thus assisting to per- 

 petuate his memory are themselves honoured in the 

 act. 



NO. 1236, VOL. 48] 



MODERN MYCOLOGY} 



IT is not often that a great and industrious investigator 

 lives to see his chief work so far completed as Prof. 

 Brefeld has done ; and still more rarely to find an enthu- 

 siastic exponent of all his views so willing and so capable 

 of putting them before the public as Dr. von Tavel here 

 proves himself to be. 



It is hardly thirty years ago since the late Prof, de 

 Bary of Strasburg showed that the study of the fungi. 



up to that time a chaos of statements m which the stu- 

 dent usually lost himself hopelessly, was capable of being 

 made not only a very scientific and important branch of 

 Botany, but also a very interesting one, and that there 

 were already workers in the field — especially the 

 Tulasn^s — who were showing how to do this, by patient 

 and thorough investigations of each species that could be 

 properly studied. 



De Bary himself founded a school of exact inquirers, 



1" Verg'eichenJe Mor, holog'e" dor Pilze." By Dr. F. Von T.ivtl 

 (Jena ; Fisclier, i8ga ) 



