3J. 



KNOWLEDGE. 



[Februaky 1, 1897. 



THE_ | y/\\ [ScIpCE 



OF THE ] ^ 



i QUEEN'S REIGN 



k^^S4 



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SIXTY YEARS OF ASTRONOMICAL RESEARCH. 



By Miss Agnes M. Clerke, 



Authoress of " The Systeyn of the Stars," and " A Popular 

 History of Astronomy during the Nineteenth Century," Sc, dc. 



THE progress of astronomy since the accession of 

 the reigning sovereign has been, on one side, a 

 development; on the other, a metamorphosis. 

 While the traditional methods have been improved, 

 and traditional aims pursued with ever-increasing 

 dihgence, novel methods have come into use — novel 

 methods of such transforming power that the science has, 

 in a measure, changed its aspect and attitude. Sixty 

 years ago it stood apart, in close alHance with mathematics. 

 Now it appeals for aid to chemistry and optics, to electrical, 

 thermal, and molecular investigations. Every new fact 

 ascertained in a laboratory has a bearing upon some 

 cosmical problem ; every well-groimded theory of matter 

 and force finds its application in the heavens. These 

 intricate relations possess a significance as yet imperfectly 

 apprehended ; they may lead to generalisations of a higher 

 order than any so far attained. Their establishment is 

 the cardinal event in recent astronomical history. 



Astrophysics took its rise in 1851 from Schwabe's 

 discovery of the sunspot period ; for it was quickly perceived 

 that the magnetism of the earth, including auroral displays, 

 obeyed an identical law of change. Thus, terrestrial 

 phenomena acquired an universal import, and became 

 affiliated to cosmical vicissitudes. The chemical inter- 

 pretation given by Kirchhoil to the hieroglyphics of the 

 solar spectrum drew the connecting bonds closer. He 

 announced to the Berlin Academy of Sciences, December 

 15th, 1859, the presence in the sun of sodium, iron, 

 magnesium, calcium, and some other familiar metals. 

 The evidence warranting these identifications was the 

 agreement of certain " Fraunhofer lines " with the 

 individual rays given out by the glowing vapours of 

 the substances in question, coupled with the fruitful 

 root-principle of the correlation of emission and absorp- 

 tion. The position of each isolated ray in the dispersed 

 Ught of a heavenly body was thus shown to be indicative 

 of its constitution, and the impossible — as Comte had 

 declared acquaintance with such facts to be — was achieved. 

 The science of astrochemistry developed rapidly. About 

 thirty-six elements, including hydrogen and carbon, have 

 been recognized as common to sun and earth, and those 

 missing need not be supposed absent. Three among them — 

 antimony, bismuth, and mercury, all heavy metals — early 

 declared themselves in the red stars, Aldebaran and 

 Betelgeux ; and some fine lines belonging to oxygen — a long- 

 sought and evasive substance — have apparently just been 

 picked out by Eimge and Paschen from Mr. Higgs's solar 

 spectral. photographs. Undetermined lines, however, still 

 abound in celestial spectra, to an extent, it might almost 



have been thought two years ago, seriously compromising 

 the prospects of advancing knowledge. But Prof. Ramsay's 

 enfranchisement fi-om its miUenniaJ prison in a Norwegian 

 mineral of the solar gas helium, has effectually dissipated 

 these misgivings. Its highly complex spectrum figures 

 bright in the solar chromosphere, in nebula^ and temporary 

 stars; dark, in a restricted class of white orbs, a complete 

 battalion of which are arrayed in the constellation Orion. 

 The chief -nebular constituent has not, so far, been 

 "imearthed"; nor " coronium," a gas probably lighter than 

 hydrogen, which pervades the solar halo. They may, never- 

 theless, be found any day hibernating in the earth's crust. 



The stars were, in 1863, brought by Dr. Huggins and 

 Prof. W. A. Miller within the scope of Kirchhoff's con- 

 clusions. Their chemistry proved to be generically the 

 same with that of the sun, although with decided specific 

 differences. They were divided by Father Secchi into four 

 spectral orders ; and his classification has been in the main 

 adhered to by Prof. Vogel, who added the "rationalising" 

 idea of decline with increasing age, from the culminating 

 splendour of the Sirian type, through a solar stage, to the 

 waning fires of red stars showing banded spectra. His 

 scheme of decay was enlarged into a scheme of development 

 by Mr. Lockyer, who begins at the beginning with the 

 nebula? ; but it is unlikely that time is the sole factor in 

 producing the observed varieties of sidereal species. 



Dr. Huggins began his investigations of nebular spectra 

 on August 1st, 1864. The first he looked at consisted of one 

 bright and two fainter green rays, the most refrangible being 

 the " F" of hydrogen. He had selected for examination 

 the " planetary" in Draco, and all nebula of that kind, as 

 well as those of u-regular shape like the great formation 

 in Orion, are of gaseous constitution. But he soon found 

 that most nebuLp, and notably the vast ellipse in Andro- 

 meda, give a continuous spectrum such as might be derived 

 from distant star-clusters. The manner of their distribution 

 separates them emphatically, nevertheless, both from 

 gaseous objects and from true clusters, the latter two 

 classes belonging characteristically to the zone of the 

 Milky Way, while ordinary nebulse gather towards its 

 poles. This architectonic relation proves them to make 

 an integral part of the galactic system, and is one among 

 many reasons elicited by modern research for rejecting 

 the claim to autonomy as " island universes " long ago 

 set up for them by Kant. 



The rapid progress of astronomy in our time along the 

 old no less than the new lines of research, has been largely 

 due to its adoption of photography as an ally. The services 

 which this wonderful art has proved capable of rendering 

 have distanced hope. The staying power of the chemical 

 plate, its faculty of waiting upon time and integrating 

 infinitesimal impressions, has led to the partial abdication 

 in its favour of the human eye. It has the further pre- 

 rogatives of sensibility to invisible light, of swiftness in 

 procedure, and of affording permanent and absolutely 

 truthful records. There is no imagination behind it. The 

 addition of these powers to astronomical resources has 

 effected a revolution unique in the history of science, and 

 still actively advancing. Its consequences are unexhausted, 

 and apparently inexhaustible. 



Celestial photography is predominantly employed in four 

 departments of inquiry : in direct portraiture, in the dis- 

 covery of new objects, in star-charting, and in the delineation 

 of spectra and spectral forms. The various results can 

 here be no more than barely indicated. Warren de la 

 Rue was the earliest promoter in this country of solar and 

 lunar photography. AVith his " photoheliograph " the 

 daily registration of sunspots was begun at Kew in 

 1858 ; and the same instrument served, during the 



