August 31, 1906.] 



SCIENCE. 



271 



of that relation being a large problem for 

 future study, while as an immediate conse- 

 quence of the altered concept we have doubt 

 cast upon the supposed determinations of the 

 sun's motion in space. At this point, as in 

 most discussions of the kind, we miss a frank 

 recognition of the relativity of all motion, 

 and its corollary that the direction and ve- 

 locity of the motion to be imputed to the sun 

 is purely a matter of convention and defini- 

 tion, depending upon the choice of an origin 

 to which that motion shall be referred. The 

 author appears to regard the solar motion as 

 something fixed in the order of nature, which 

 should be found always the same, barring acci- 

 dental errors, from any considerable group of 

 stars used for its determination. 



To the non-professional reader, doubtless, 

 the most interesting part of the work will be 

 found in the third section, devoted to the con- 

 struction of the heavens. Without ignoring 

 the work of others, Easton, Kapteyn, Schia- 

 parelli, Stratonoff, etc., Seeliger's discussion 

 of the distribution of the Durchmusterung 

 stars here plays the principal role and is de- 

 scribed by the author as ' a complete solution 

 of the problem ' ; which * determines the uni- 

 verse as revealed to us in the enumeration of 

 the stars,' etc. The character of the finite 

 and definitely limited universe thus revealed 

 is described as follows: 



Throughout a finite space of spherical form 

 there are distributed bodies of widely varying 

 mass and widely varying physical condition. 

 Amidst gaseous nebulae of extraordinarily low 

 temperature are placed other bodies strongly con- 

 densed and glowing hot. The arrangement of 

 these individual masses is not one of haphazard 

 uniformity, but, as swarms, they are clustered 

 about individual centers which, in loose relation 

 one to another, are arranged in the shape of a 

 great spiral with multiple arms. In the re- 

 moter parts of this spiral the hotter and gaseous 

 stars predominate, while near the center of the 

 spiral is the sun and its more closely related 

 stars, which for the most part resemble it in phys- 

 ical condition. Many of these latter share in 

 the motion of the sun along the fundamental plane 

 of the spiral, i. e., the milky way. There are also 

 numerous other groups of stars possessing a 

 common motion in the plane of the galaxy. 



The doctrine of a demonstrably limited 

 stellar system thus presented is avowedly based 

 upon statistics of the distribution of stars 

 brighter than the tenth magnitude, and as 

 these stars constitute, both in number and 

 extent, only a small fraction of the visible 

 universe one is tempted to question the sound- 

 ness of that logic which extends to the larger 

 aggregate, conclusions of an empirical char- 

 acter derived from a minute fraction of the 

 whole. Indeed, conservatism in this respect 

 seems the more required, since, as is conceded 

 by Kobold, the apparent distribution of the 

 fainter stars is quite unlike that of those 

 from which his conclusions are drawn. Even 

 for these brighter stars it is probable that the 

 supposed indication of a limited and finite 

 system is fallacious and arises from the tacit 

 assvmaption that the fainter stars appear faint 

 only by reason of their greater distance from 

 the earth. It has been recently shown that 

 such is not the case, the stars of the fainter- 

 magnitudes being intrinsically less luminous 

 than those of the brighter classes. 



At page 215 of the text Dr. Kobold falk 

 into serious error in comparing Kapteyn's 

 empirical formula for the probable parallax 

 of stars of determined proper motion and 

 brightness with Comstock's determination 

 0.0045", as the mean parallax of a consider- 

 able group of stars of the average magnitude 

 10.5. According to Kobold, 'Kapteyn's Formel 

 nur 0.0016" verlangt/ for this group of stars, 

 while in fact the formula furnishes for this 

 case 0.0042", in excellent agreement with the 

 observed value. It is only justice to Dr. Ko- 

 bold to state that no other similar case has 

 come within the reviewer's note. 



G. C. C. 



SCIENTIFIC JOURNALS AND ARTICLES. 



The American Naturalist for August con- 

 tains articles on 'Volant Adaptations in 

 Vertebrates,' by E. S. Lull; 'External Mor- 

 phology of the Dugong,' by H. Dexler and 

 L. Freund, and ' Eeproduction of Metridium 

 marginatum by Eragmental Eission,' by M. L. 

 Hammatt. Dr. Lull notes that volant evolu- 

 tion has occurred seventeen times, seven of 

 these , instances being for true flight. Dr. 



