434 



NATURE 



[March 9, 1893 



The problem of the stratification of the sun's atmosphere 

 does not, therefore, appear to have been advanced by his 

 discussion of the various observations. 



Dr. Brester's view of the solar surroundings leads him 

 to suppose that the concentric layers which he postulates 

 are ellipsoidal, so that the photosphere cuts different 

 shells in different latitudes. The fact that there is an 

 equatorial extension of some sort is abundantly demon- 

 strated by eclipse photographs. In the application of 

 this view to the explanation of some of the phenomena 

 presented by the sun Dr. Brester displays considerable 

 ingenuity, and we may refer to some of them, as they 

 suggest points which may have to be taken into con- 

 sideration in other theories. 



The Solar Rotation. — It is a matter of common know- 

 ledge that the equatorial regions of the sun, as indicated 

 by the spots, rotate more rapidly than the regions in higher 

 latitudes. On Mr. Lockyer's hypothesis, which supposes 

 sun-spots to be produced by the fall of condensed materials 

 from the cooler regions of the atmosphere, this is ex- 

 plained by the fact that such atmosphere is highest at the 

 equator, and the spot-forming matter thus having a greater 

 forward velocity previous to its descent, will have a greater 

 angular velocity on reaching the photosphere. Dr. Bres- 

 ter's view is a modification of this. Taking for granted 

 that the solar layers are ellipsoidal, and that the photo- 

 sphere is an independent partially condensed shell, he 

 points out (p. 44) that when the matter of any particular 

 layer condenses to form a part of the photosphere, the 

 increase of density will cause it to descend towards lower 

 layers, and as it will retain its initial velocity, the angular 

 velocity in its new position will be increased. In this way 

 he explains the law of solar rotation, but on account of the 

 absence of knowledge of the densities of the vapours near 

 the photosphere, the question cannot be treated mathe- 

 matically. On Dr. Brester's view this law applies only to 

 the photosphere itself, the ellipsoidal layers all having 

 the same angular velocity. 



This he further applies to the reconciliation of the 

 spectroscopic determinations of the velocity which have 

 been made by Duner and Crew. Dundr's observations 

 practically confirm the law derived from the observations 

 of spots, while those of Prof. Crew show no change of 

 velocity with change of latitude. Dr. Brester points out 

 that most of the lines observed by Crew have been seen 

 bright in the chromosphere, while those observed by 

 Duner have not been so recorded. Hence he concludes 

 that the lines observed by Duner are produced by the 

 absorption of vapours actually lying in the interstices of 

 the photosphere— and therefore indicating the same 

 velocity— while those observed by Crew show only the 

 uniform angular velocities of the ellipsoidal shells. 



Changes in the Spectra of Sun-spots.— V)x. Brester's 

 theory also gives an explanation of differences in the 

 spectra of sun-spots at different parts of the spot-period. 

 Observations have shown that at maximum the lines 

 which are most widened in spot-spectra are chiefly lines 

 of unknown substances, while at minimum they are chiefly 

 lines of iron and other known substances. When it is 

 remembered that there is a progression in latitude with 

 the advance of the spot-period, Dr. Brester's view can 

 readily be understood ; the photosphere in each latitude 

 will have a different composition, and hence change of 

 NO. I 2 19, VOL. 47] 



latitude will be accompanied by change of spectrum. It 

 is only fair to say that the exact nature of this change has 

 not yet been fully investigated, and hence the explanation 

 offered cannot strictly be put to the test. Broadly speak- 

 ing, however, it is evident from what has already been 

 said, that if Dr. Brester's view be correct, there must be 

 a layer of unknown vapours cutting the photosphere about 

 latitude 15" (the latitude of spots near maximum), and 

 layers of the vapour of iron, or some of its constituents, 

 cutting the photosphere about latitudes s'' and 30'' (the 

 latitudes of spots at minimum). ' Before the view can be 

 properly tested, it is clear that we must have further 

 knowledge as to whether the iron lines widened in spots 

 of high latitude at the beginning of a sun-spot period are 

 identical with those widened in spots near the equator 

 towards the end of the period, and, so far as we know, 

 information on this point is wanting. 



The Periodicity of Solar Phenomena.— 'Dr. Brester 

 first of all dismisses the suggestion of planetary disturb- 

 ances as the phenomena usually seen are too irregular 

 to be consistent with orbital motion ; and other views 

 are also found wanting. He then shows how the second 

 of the astrochemical principles already referred to appears 

 to him to give the necessary explanation. As in our 

 notice of his first essay, we may say that the main idea 

 is that during eleven years the integrated effects of the 

 various chemical combinations which have taken place 

 are such as to very nearly restore the conditions 

 which had existed at the commencement of the period. 

 Slight differences would be produced each time, so that 

 after a long interval wide differences might be expected. 



Many other problems are discussed, and Dr. Brester 

 has satisfied himself that his theory is competent to 

 explain them all. Want of space, however, will not per- 

 mit further reference. 



The volume will be a valuable one, if only for thesfact 

 that it brings together a great mass of work which has 

 been done in connection with the sun— over 300 authors 

 being quoted — and although we are not prepared to 

 accept his theory in all its points, it is fair to say that 

 some of his arguments are extremely suggestive, and may 

 help in time to unravel some of the mysteries of our 

 central luminary. 



In subsequent communications Dr. Brester will 

 extend his theory to the phenomena presented by variable 

 stars, comets, and other celestial bodies. A. F. 



ELEMENTARY BIOLOGY. 

 A Course of Practical Elementary Biology. By John 

 Bidgood, B.Sc, F.L.S. (London: Longmans, Green, 

 and Co., 1893.) 



THIS book deals with certain of the types of animals 

 and plants which are included in other elementary 

 works on the same subject. The forms selected are 

 yeast, protococcus, bacteria, mucor, penicillium, chara, 

 fern, flowering plant, amoeba, vorticella, paramoecium, 

 hydra, mussel, crayfish, and frog. The author states that 

 "the subjects dealt with cover most elementary biological 

 courses, but apparently do not exactly fit any." The 

 work has, therefore, at any race, the merit of not having 

 been written merely from the point of view of any particular 

 examination syllabus. A certain amount of originality 



