Oct. 17, 1878] 



NATURE 



645 



chronometer, and the exact level of the slide containing 

 the sensitized plate is observed with an accurate clinometer 

 before removing it from the camera. 



As M. Janssen has pointed out, the chemical prepara- 

 tion and development of the plate require very great care, 

 in order to obtain the requisite sharpness of detail. The 

 gun-cotton for the collodion is prepared at a high tem- 

 perature (70° C), and numerous precautions are taken to 

 •ensure that the collodion film shall be perfectly even, and 

 free from the smallest speck of foreign matter. The 

 image is developed gradually, beginning with a solution 

 •of ferrous sulphate, and after thorough washing, com- 

 pleting with a solution of pyrogallic acid, after which the 

 image is strengthened with a mixture of pyrogallic and 

 silver nitrate solutions. 



In a favourable state of the atmosphere, the pictures 

 ihus obtained leave nothing to be desired in point of 

 sharpness and definition of detail. But, as a matter of 

 course, all states of the atmosphere do not permit of 

 •equal success, the process being subject to the same 

 atmospheric contingencies as in all astronomical work 

 with the telescope. The best results were obtained in the 

 late autumn, and during this last spring. 



The character of the photospheric surface as displayed 

 in the new photographs, will be best described in a 

 translation of M. Jaiissen's own words: "The photo- 

 graphs show that the solar surface is covered everywhere 

 with a fine granulation. The forms, dimensions, and 

 arrangement of the granular elements are very varied. 

 Their size varies from some tenths of a second to three 

 •or four seconds. The shapes are circular or elliptical, 

 and more or less elongated ; but often these regular forms 

 are more or less distorted. The granulation is exhibited 

 everywhere; and, at first sight, it does not appear to present 

 a different constitution towards the polar regions. But 

 this is a point to be further investigated. The illumi- 

 nating power of the granular elements, taken separately, 

 varies much ; they appear to be situated at different 

 depths in the photospheric layer. The most luminous of 

 them, those which more especially contribute to the lumi- 

 nosity of the photosphere, occupy but a small fraction of 

 the surface of the sun. 



"But the most remarkable result yet obtained, and 

 which is exclusively due to the employment of the photo- 

 ^aphic method, is the discovery of the photospheric net- 

 work {reseaii photospheriqtce). An attentive examination 

 of the photographs shows that the photosphere has not 

 an uniform structure throughout, but is divided into a 

 series of figures, more or less distant from one another, 

 and exhibiting a special constitution. These figures 

 generally have rounded contours, but also often recti- 

 linear and sometimes polygonal. Their dimensions are 

 very variable, and they sometimes attain to a minute or 

 more in diameter. While, in the intervals between these 

 iigures, the grains are distinct and definitely bounded, 

 although of very variable size; in their interior, the 

 granules are half obhterated, drawn out. and confused; 

 most frequently, indeed, they have disappeared, giving 

 place to trains of matter which replace the granulations. 

 Everything indicates that, in these spaces, the photo- 

 spheric substance is subject to violent movements which 

 have confounded the granular elements. . . . This fact 

 enlightens us as to the forms taken by solar activity, and 

 shows that this activity is always very great in the photo- 

 sphere, even though there be no spot visible on the sur- 

 face. I will further draw attention to this very important 

 fact, of which very distinct evidence is furnished by cer- 

 tain photographs, viz., that numerous very dark points 

 appear in the regularly granulated tracts, indicating that 

 the photospheric layer can have but a very small thick- 

 ness." 



In another paper, Mr. Janssen deduces some further 

 conclusions of interest. He observes : — 



"If the solar layer which forms the photosphere were 



in a state of repose and perfect equilibrium, it would 

 result from the fact of its fluidity, that it would form a 

 continuous envelope around the solar nucleus. The 

 granular elements would be confounded together, and 

 the lustre of the sun would be uniform in all its parts. 

 But the ascending gaseous currents do not admit of this 

 state of perfect equilibrium. They break up and divide 

 the fluid layer, escaping at a great number of points. 

 Hence results the formation of the granular elements, 

 which are but so many fractions of the photospheric 

 envelope, and which tend to take a spherical form, in 

 virtue of the gravity of their constituent parts. . . , But 

 even this state of equilibrium of the individual parts is 

 but rarely realised ; in numerous points, the currents 

 drag along with them the granular elements, and these 

 latter lose their spherical form, and eventually become 

 no longer recognisable where the movements are most 

 violent. . . . Moreover, in the regions of relative calm, 

 the movements of the photospheric medium do not allow 

 the granular elements to arrange themselves in an even 

 layer, whence results the greater or less immersion of the 

 grains beneath the surface, and consequently, owing to 

 the great absorptive action of the medium, the great 

 differences of their lustre shown in the photographic 

 pictures, . . , We may further conclude, from the fact 

 of the relative rarity of the most luminous grains in the 

 photographs, that the illuminating power of the sun is 

 due principally to that of a small number of points on 

 his surface. In other words, if the solar surface were 

 completely covered with granular elements of equal bril- 

 liancy with these, its illuminating power, according to a 

 first approximate estimate, would be from ten to twenty 

 times greater than it is." It will be interesting to ascer- 

 tain, at the next epoch of sun-spot maximum, whether 

 the brilliant granules occupy a relatively larger proportion 

 of the solar disc than at the present time. The direct 

 evidence which such an observation will afford on the 

 important question of the periodic variation of solar 

 radiative intensity, a question on which much diversity of 

 opinion still exists, will be of the highest value. 



H, F. Blanford 



BIOLOGICAL NOTES 

 The Anatomy and Affinities of the Ave-Aye.— 

 Dr. Alix having recently dissected a young male Aye-aye 

 {Chiromys Madagascariensis), communicates, through 

 Prof. Gervais, to the Academy of Sciences of Paris 

 {Comptes Rendits, July 29, p. 219), soma notes on certain 

 points in its anatomy which bear upon the much-vexed 

 question of the position of this curious animal in the 

 mammalian series. It seems that his observations confirm 

 in all points the opinion of all those eminent naturalists 

 who, in accordance with De Blainville, and contrary to 

 Gmelin and Cuvier, have held that the Aye-aye must 

 be approximated to the lemurs and separated from the 

 rodents, fi'csh facts being brought forward in support 

 of this view. First, as regards its myology. The extensor 

 communis hallucis, which in rodents is attached to the 

 outer condyle of the femur, arises in the Aye-aye from 

 the tibia. The biceps brachialis, which has only one 

 head in the majority of rodents, has two in the Aye-aye. 

 The supinator longus, which is generally absent in the 

 rodents, has in the Aye-aye a good development. THe 

 common extensor of the digits, to those of the hand or 

 foot, is composed of two distinct fascicles, of which one 

 furnishes the tendons of the second and third digits, the 

 other those of the fourth and fifth, from which it results 

 that the Aye-aye, like the other Lemurina, possesses a 

 paired digital system, and resembles in this feature the 

 cloven-hoofed Pachyderms and the Ruminants, while the 

 other mammals have, under all relations, an unpaired 

 digital system. Dr. Alix has, moreover, verified the pre- 

 sence of a rotator muscle of the fibula, previously men- 



