496 



NATURE 



[September 23, 1897 



The photographs obtained by employing the above- 

 mentioned instrument and metnod were, as a rule, of 

 o 30 metres diameter, but for special purposes diameters 

 of 0*50 and 070 have been used. Some of these pictures 

 have been beautifully reproduced in the volumcbefore us, 

 and surpass any others that have been obtained both in 

 clearness and fineness of detail. 



A minute examination of such photographs has greatly 

 enlightened us on many points regarding the surface 

 movement and appearance of the photosphere, and in the 

 near future we shall have series of photographs taken 

 very quickly one after another, which will help us to 

 follow the motions, invisible even to the unaided eye, 

 most closely. 



Further, it has been shown that the forms, dimensions, 

 and distribution of the granulations are not in accordance 



Fig. 2. — A jortion ot t'.ie 



olar surface, showing a sunspot and a mean 

 exu (June 22, 1885). 



with the ideas formed of these elements of the photo- 

 sphere as seen through telescopes. The photographic 

 images do not confirm the notion that the photosphere 

 is built up of elements, the forms of which are constant, 

 and resemble rice grains, &c. The granulations, accord- 

 ing to M. Janssen, assume dififerent shapes under different 

 circumstances, and vary very much in size. 



The discovery of the photospheric reseau is another 

 outcome of the Meudon photographs. A close study of 

 the photographs showed that the photosphere was not 

 uniformly constituted in every part, but that it was 

 divided into series of figures more or less separate from 

 one another, and exhibiting a peculiar structure. The 

 sizes of these figures were found to vary, and their con- 

 tours were more or less rounded, sometimes rectilinear, 

 and very often polygonal. These different types of 

 reseaux are clearly seen on the photographs in the 

 volume, and one of these, illustrating a mean type of 

 NO. 1456, VOL. 56] 



rheaii, is given in the reproduction accompanying; 



this article (Fig. 2). 



The picture, here considerably reduced, was taken on 

 June 22, 1885, the diameter of the disc being o-888 

 metres, and gives a good idea of what is meant by a 

 mean reseau. The photograph shows, further, a large 

 spot, the principal nucleus of which measured nearly two 

 minutes of arc in diameter. The faculae and stride of the 

 penumbra of the spot illustrate very clearly that these 

 parts were formed of granulations like the rest of the 

 solar surface. 



A special inquiry as to the distribution of this granu- 

 lation over the entire solar surface brought out the fact 

 that even at the poles it was quite distinguishable ; it 

 thus differs from the spots, which are limited to two 

 narrow belts on each side of the solar equator. 



The last sections of the volume are devoted to several 

 other uses of solar photography, as, for instance, the 

 questions of the presence of a lunar atmosphere, or of small 

 bodies passing between the earth and the sun. Both of 

 these have been investigated at Meudon, and in each case 

 a negative answer was the outcome of the research. 



In bringing this notice to a conclusion, we may remark 

 that this, the first volume of the "Annals," is worthy of 

 the institution from which it hails, besides being a valuable 

 contribution to astronomy. It is, perhaps, the most hand- 

 some volume of any " Annals " which it has been our 

 lot to notice, and the numerous reproductions of photo- 

 graphs are models of what can be accomplished in this 

 line of work. 



The French Government is to be congratulated on 

 being the means by which such fine work in astronomical 

 science can be accomplished, and is, we have no doubt, 

 proud of the able director to whose energy and skill 

 such important advances are due. 



William J. S. Lockyer. 



RECENT WORK OF THE UNITED STATES 



GEOLOGICAL SURVEY. 

 •T^HE Fifteenth Annual Report of the United States 

 *■ Geological Survey opens with a few words of fare- 

 well spoken by the Director, Major Powell, on his retire- 

 ment. Modestly and briefly he reviews some of the 

 work done by himself and his colleagues, which has been 

 expressed in not less than a thousand maps and two 

 hundred volumes. The last Report issued by him is a 

 worthy successor of the earlier ones in material and in 

 illustrations ; many of the latter are exceptionally fine, 

 and show what can be done by the artistic printing on 

 high-class paper of blocks processed from good photo- 

 graphs. When will English officialdom learn that the 

 thousands of pounds spent in promoting research lose 

 nine-tenths of their effect on account of the slovenly and 

 imperfect presentation of the results to the public ? 



One of the most interesting memoirs in this volume,^ 

 on the Granites of Central Maryland, is prefaced by a 

 short but very able chapter from the pen of Prof. G. H. 

 Williams, whose promising life has been cut off in its 

 prime. Here we see evidence of a firm grasp of his 

 subject, with knowledge and experience amongst the 

 class of rocks with which he deals, and the ability not 

 only to acquire and assimilate the work of other 

 observers, but to show clearly that towards the end 

 attained not only himself but a host of other workers 

 have contributed. 



Evidence from apophyses, chilled margins, contact 

 metamorphism, and inclusions, as well as from the ulti- 

 mate chemical and mineralogical constitution of the 

 rocks, is all effectually used to demonstrate that these 

 rocks are igneous products ; the close association of a 

 wide range of petrographic types is evidence pointing to 

 the same conclusion. The pegmatites are studied in 

 detail, and a conclusion arrived at that in this district 



