August 1, 1892.] 



KNOWLEDGE 



151 



DOUBLE STAR ORBITS. 



To the Editor of Knowledge. 



Sir, — I am glad to hear that Mr. See is about to publish 

 a fuller exposition of his views as to the orbits of double 

 stars. I ask leave to add a few words, however, in order 

 that my objection may be more completely dealt with in 

 his forthcoming worli. I think I am correct in saying that 

 equality (or a near approach to equality) of mass is onr of 

 the circumstances which, in his opinion, tends to produce 

 the high eccentricitv of binary star orbits ; and if this be 

 so, we ought to obtain on the nivroiir a higher eccentricity 

 for binaries with equal than with unequal masses. I did 

 not, of course, intend to apply this reasoning to each 

 individual case, but I think the average in the two cases is 

 about the same. 



A point of considerable interest raised by Mr. See is that 

 of the age of a binary system. It would follow, I think, 

 from his principles that the orbits of the close binaries 

 recently discovered by the spectroscope should be pretty 

 nearly circular. Further spectroscopic observation may 

 throw light on this subject. All the spectroscopic binaries 

 or variables of the Algol type have, so far as I know, spectra 

 of the first type. From this we might, perhaps, infer that 

 binaries with this spectrum, like Sirius and Castor, were 

 of more recent date than binaries with spectra of the 

 second (or solar) type, and that consequently their orbits 

 should be on the average less eccentric. I doubt whether 

 this is so. 



We are, unfortunately, unable to observe the effects of 

 nearly equal masses in the binaries within the solar system. 

 The earth and moon are not far from the closest approach 

 in the case, but the ratio of the masses is eighty to one. 

 Is the mass of Neptune's satellite known ? 



Truly yours, 



W. H. S. MoNCK. 



Notice of ISoolt. 



Island Lit I- . By Alfi-ed Russel Wallace. Second Edition. 

 (MacmiUan & Co.) — It is about sixteen years since Mr. 

 Wallace laid the foundations of that branch of combined 

 biological and geographical science with which his name 

 will always be associated, by the publication of his great and 

 comprehensive work on the "Geographical Distribution of 

 Animals," a work followed in the course of four years by a 

 smaller volume containing a further exposition of his views 

 with regard to insular faunas and floras, and entitled "Island 

 Life." Now, after a further interval of twelve years, 

 we have a second edition of the latter work, and it is pretty 

 good evidence of the general soundness of the principles 

 originally enimciated that the author has practically 

 nothing to retract, and scarcely anything of his original 

 arguments e.ven to modify. The changes consist chiefly of 

 additions to the stores of facts already recorded about the 

 plants and animals of Great Britain, .Japan, the Galapagos, 

 the Sandwich Islands, Borneo, Madagascar, and New 

 Zealand, and these are the results of observations made 

 since the issue of the first edition. No better illustration 

 could be given than this book affords of the marvellous 

 change that has been introduced into biological studies, 

 and the immense amount of additional mterest that has 

 been imparted to them by the abandonment of the idea of 

 the fixity of species, and the acceptance of the principles 

 of natural selection and evolution. To one who imagined 

 that each species had been specially formed in the region 

 it now inhabits, and had always existed there since its first 

 formstJiion, what could have seemed more dry and 

 uninteresting than a catalogue of the fauna and flora of a 

 district '? On the other hand, to the thoughtful evolutionist 



who recognizes that the whole of the present condition of 

 things is a product brought about by the inter-action 

 through long ages of various more or less opposing 

 influences, the very reverse is the case, and every name in 

 such a list becomes encircled with a halo of romance as the 

 questions arise. How came this organism to be what it is, 

 and where it is "? What past changes in its surroundings 

 does it bear witness to ? How can it be used to help to 

 unravel the tangled skein of the primeval history, both of 

 its race and of its present dwelling-place "? And these are 

 the questions which are ever kept in view by the author of 

 " Island Life," whence arises in the experience of the 

 reader a mental invigoration and stimulus as he 



' follows the clear exposition of the argument. 



Islands, in consequence of their restricted area and definite 

 boundaries, and the barrier the surrounding seas offer to 

 the migration of many organisms, are specially well 

 adapted for the study of questions connected with the 

 distribution of animal and vegetable life. But from the 

 point of view of the naturalist, there are remarkable 

 differences between islands, depending upon the time and 

 method of their origin. The Britisli Isles well illustrate 

 one of these types, that of the recent continental, the ' 

 comparative shallowness of the water that separates them 

 from the Continent indicating that their severance took 

 place at no very remote period. The plants and animals 

 accordingly show a close resemblance to those of the 

 Continent, and there does not appear to have been time 

 enough for the production of more than a few distinct 

 forms. From our poverty in indigenous species of the 

 larger animals, Mr. Wallace argues that the connection of 

 Great Britain with the Continent, after the last glacial 

 period had exterminated the previous and richer fauna, 

 was of short duration ; thus, while Germany has nearly 

 ninety species of land mammalia, Britain, having been early 

 cut off, has only forty ; it has also a still smaller proportion 

 of reptiles and amphibia. In none of these cases has the 

 effect of their isolation been such as to produce a distinct 

 species or even variety. Amongst birds, however, we 

 have the red grouse of the northern moors as a peculiar 



i species, as well as two peculiar varieties of tits ; whUe our 

 lakes yield a goodly number of fishes which are found 

 nowhere else. The insect fauna exhibits more striking 

 peculiarities. A list of eighty-nine species and varieties of 



■ butterflies and moths is given, which, so far as present 

 knowledge goes, are confined to Britain. These include 

 the splendid "large copper" butterfly, the glory of the 

 old collectors, but now, alas, extinct. Of beetles, again, 

 sixty-seven are enumerated which have not been dis- 

 covered elsewhere. Too much reliance, however, must 

 not be placed on these numbers, for it may well be that 

 many of these insects, especially the smaller species, have 

 hitherto been overlooked on the larger area of the Con- 

 tinent, and may be expected yet to turn up there. This 

 seems the more likely to be the case, inasmuch as, although 

 fifteen additional species have been included since the first 

 edition of '• Island Life " was published, there have been 



' a still larger number removed from the old list in conse- 



' quence of their having been since found on the Continent, 

 so that the total number of apparently peculiar beetles 

 is actually reduced from seventy-two to sixty-seven. 

 Whatever allowances be thus made, however, there 

 still remains, as Jlr. Wallace points out, enough to dis- 



'• tinguish our insular fauna from that of the Continent. 

 The case of Madagascar is a great contrast to this ; 

 here we have an island separated by deep water from the 

 adjacent continent, indicating a much more ancient separa- 

 tion, and consequently there is much greater dissimilarity 

 in the types of both animal and vegetable life ; in fact, the 



