February 13, 1902] 



NA TURE 



351 



photographs of objects in their natural surroundings. The 

 lantern slides sent by Messrs. Sanders and Crowhurst are 

 from photographs of birds, nests, eggs and young and other 

 living animals taken by Mr. Oliver G. Pike. To lecturers on 

 natural history such true pictures of living creatures must be 

 invaluable, and no better source of encouragement to study 

 nature could be desired. By the side of such beautiful photo- 

 graphic pictures as are now available for projection upon a screen 

 or for the illustration of books, the drawings which did duty 

 in natural history instruction seem but a vain show. Messrs. 

 Sanders and Crowhurst send us with their slides an ingenious 

 arrangement for viewing lanterij slides under a low magnifying 

 power. The arrangement, though simple, is very effective, and 

 a pleasant half hour can be passed byjusing it to look at lantern 

 slides. ■ 



The additions to the Zoological Society's Gardens during the 

 past week include a Greater Vasa Parrot (Coracopsis vasa) 

 from Madagascar, presented by Lady Amherst of Hackney ; a 

 Black-footed Penguin [Spienisciis demersus) from South Africa, 

 presented by Lieut. F. J. Mosely ; a Black-headed Gull (Lants 

 ridibundiis), European, presented by Miss M. Hall ; a Bataleur 

 'EdL^e (Htlotarsus ecaudattis) hom Lagos, presented by Mr. J. 

 Peacock ; two Yellow-cheeked Amazons (Ckrysotis aiititmnalis) 

 froni; Honduras, two Wall Creepers (Tichod)omus muraria), 

 European; deposited. 



OUR ASTRONOMICAL COLUMN. 

 Disturbance of Corona in Neighbourhood of Promin- 

 ences. — Prof. C. D. Perrine, who had charge of the expedition 

 to Sumatra organised by the staff of the Lick Observatory to 

 observe the total eclipse of the sun on May l8, 1901, gives in 

 his report a preliminary description of the results obtained in the 

 Astrophysical Journal, vol. .xiv. pp. 349-359. From a short e.\am- 

 ination of the photographs of the corona obtained with the forty- 

 foot and Floyd telescopes (which are stated to show the details of 

 the inner corona very perfectly in spite of the presence of clouds 

 during the exposure), there is distinct evidence of disturbances 

 in certain areas of the coronal structure. Especially noticeable 

 is a conspicuous series of coronal hoods surrounding a promin- 

 ence in position angle 115', and also an unusual appearance in 

 the north-east quadrant of the corona. This latter is near 

 position angle 65". Close to this point on the limb there is a 

 small compact prominence, surrounding which the disturbed 

 area has a form roughly resembling an inverted cone of large 

 angle. The apex of this area is not visible, appearing to lie 

 below the chromospheric layer showing at the limb. From the 

 apparent position of the apex, a number of irregular streamers 

 and masses of matter radiate as if propelled by some explosive 

 force. A long thread-like prominence to the south of this point 

 appears to originate from the same source. Above and around 

 this region the corona is composed of broken irregular masses, 

 very similar to those depicted on the photographs of the Orion 

 and other nebulae. 



A NEW SOLAR THEORY} 



T T is a remarkable fact that in the numerous .theories which 

 -*■ have bsen propounded in explanation of the periodic changes 

 of the solar phenomena no account has yet been taken of so 

 important an element as the light- and heat-absorbing envelope 

 surrounding the photosphere. The attention which this so- 

 called solar atmosphere has hitherto received, on the part even 

 of our most eminent investigators, irf connection with the 

 economy of radiant energy on our luminary, is. utterly dispro- 

 portionate to the importance of the subject. In spite of the fact, 

 which was first accurately established by Langley's observations 

 and was afterwards confirmed by others, that the sun, if de- 

 prived suddenly of this protecting screen, would " radiate into 

 space as much as double its present amount of energy, solar 

 1 Abstract of .1 paper m Aslr.^ Nachr. (No. 37*23-24) : " Ueber eine neue 

 Theorie zur Erkiarung der'Periodicitat der solaren Erscheinungen.*' 



NO. 1685, VOL. 65] 



physicists failed to perceive that changes in the absorptive power 

 of this envelope must entail consequences of the most far-reach- 

 ing character with respect to the thermal conditions on and in 

 the sun. That such changes — and these, too, of no inconsider- 

 able magnitude — must inevitably occur is a conclusion which 

 it is hardly possible to evade when it is remembered that the 

 supreme control over the dispensation of solar energy depends 

 entirely on a thin, shallow surface-layer, the matter of which is 

 Constantly tossed about by vehement eruptions and acted upon 

 by a most complicated and powerful system of convection cur- 

 rents to and from the sun's centre. 



The possibility of variations of the opacity of the solar 

 atmosphere was, it is true, strongly urged, more than twenty 

 years ago, by one of the greatest authorities on this question. 

 Shortly after his well-known researches into the absorbing 

 faculty of the solar envelope, Langley pointed out the decisive 

 influence on the sun's radiation into space caused by changes 

 in- the transmissive power of its atmosphere. But his atten- 

 tion .was at the time solely directed towards their probable 

 effects on the temperature of our own planet. He found that 

 an increase of absorption by as much as 25 per cent, would 

 diminish the mean surface temperature of our globe by 100° F., 

 whilst a like diminution in the solar envelope would produce a 

 corresponding change in the opposite direction. 



Now if the influence of a change in the absorptive power of 

 the solar atmosphere is so enormous on a planet at a distance of 

 almost a hundred millions of miles, of what inconceivable im- 

 portance must it not be for the sun itself? Drawing the very 

 natural inference that a deficit of outside radiation means a 

 surplus of energies working upon the solar matter, and vice 

 versA, we are forcibly led to conclude that even slight changes 

 of opacity, such as would elude our most refined observations, 

 are bound to greatly influence the state of thermal equilibrium 

 on our luminary. 



Hence, if changes in the absorptive power of the sun's 

 atmosphere exist, as cannot but be the case, the question pre- 

 sents itself : What happens with those energies which, by a 

 condensation of the solar envelope, are prevented from escapiiig 

 into space? No doubt they are preserved to the sun, but in 

 what form ? Do they raise the temperature of the solar mass, 

 or augment its store of potential energy, or have they a share 

 in the generation of those marvellous dynamical displays which 

 we perceive in periodic succession on the solar surface ? Ques- 

 tions such as these must tend to convince the investigator that 

 a research into the causes of the variability of the forces which 

 we see acting on the sun, if not identical with, is at least closely 

 akin to, the investigation of the origin and the physical pro- 

 perties of the sun's atmosphere. I shall endeavour, in these 

 columns, to demonstrate the possibility of such changes in the 

 density of the solar envelope as would lead to alterations of the 

 thermal conditions of the sun's mass, and shall make an attempt 

 to answer the question as to how far these changes must be con- 

 ducive to variations in the dynamical phenomena at the sun's 

 surface. 



There is perfect unanimity amongst astronomers as regards 

 the nature of the force which by a continuous generation of 

 heat compensates for the loss of energy into Space. Helmholtz's i 

 theory, which attributes this heat-generation to the progressive 

 contraction of the solar mass as a consequence of gravitation, 

 may be regarded as one of the most probable hypotheses ever 

 propounded in the history of physical science. But this theory 

 does not yet enable us to form an idea of the evolution of a 

 celestial body. It explains the existence of a heat-generating 

 force within the star's bulk, but it gives no answer to the ques- 

 tion as to whether the loss of energy by radiation is exactly 

 compensated for by the generation of energy through contraction, 

 or whether the conditions of contraction peculiar to the sun 

 may not perhaps produce more or less heat than is required for 

 compensation. It is, indeed, inconceivable that the conditions of 

 contraction can remain the same throughout tbe lifetime of a 

 star. The spectroscope has revealed the fact that the photo- 

 spheres of different s(4rs exhibit widely difter^nt stages as regards 

 temperature. There are doubtless suns hotter than ours, and 

 others considerably cooler. And we may confidently assume 

 that the various conditions of temperature now recognised in 

 the different types of star-spectra represent the phases which 

 successively appear in the evolutioti' of eacH of these bodies from 

 its origin as a far-extended nebula down to' its complete obscur- 

 ation. In the life of each of "these stars 'there will be a period 

 whtin its temperature is on the ascent, arid when, conseqilently. 



