(6 



KNOWLEDGE, 



[Apbil, 1903. 



tendency to coalesce with the npper bones of the foot. 

 Nor is this all, for the latter bones — the metatarsals of 

 the anatomist — in some cases are partiall_y coalesced, so 

 as, in conjunction with the lower half of the ankle, to 

 approximate to that very characteristic bone of a bird's 

 leg the tarso-metatarsuK. Moreover, there are decided 

 resemblances between the haunch-bones, or pelvis, of 

 dinosaurs and birds. 



It was largely on the evidence of the dinosauriau 

 skeleton — especially that of some of the smaller members 

 of the group — that Huxley was induced to brigade birds 

 and reptiles together as Sauropsida. When this generalisa- 

 tion was made, the modern doctrine of parallelism in 

 development was not recognized as an important factor in 

 evolution ; and since its recognition doubts have been 

 expressed whether the skeletal resemblances between birds 

 and dinosaurs may not be due to this cause rather than 

 to direct genetic affinity between the two groups. By 

 parallelism in development, it may be explained, is meant 

 the production of more or less nearly identical structural 

 peculiarities by adaptation to similar, or somewhat similar 

 modes of life ; or perhaps, in some instances, to a general 

 progressive evolution towards a -higher structural type. 

 One of the best instances is afforded by the cases of the 

 horses and the prototheres, to which attention is devoted 

 in the sequel. 



With a full knowledge of the important part played by 

 parallelism in development before him, Prof. H. F. Osborn,* 

 of New York, has recently reconsidered the evidence in 

 favour of the existence in the Permian period of a common 

 ancestral stock from which have diverged dinosaurs and 

 birds. WhUe admitting that many of the resemblances 

 between these groups are adaptive rather than CTcnetic, 

 and believing that the apparent close corresijondence in 

 the structure of the jielvis between adult birds and the 

 herbivorous dinosaurs (which are specialised types) is due 

 in a considerable degree to a misinter])retation of the 

 homology of some of their elements, Prof. Osborn 

 nevertheless argues that the resemblances between the two 

 groups are so numerous as to justify the belief of kinship. 

 Special importa,nce is attached to the opinion that some 

 sort of bipedalism was a common character of all dinosaurs, 

 the suggestion being countenanced that certain forms, like 

 Stegoeaurus, have reverted from a bipedal to a quadrupedal 

 mode of pi-ogressiou. Our present knowledge, he concludes, 

 therefore, justifies us in saymg that "in this bipedal 

 transition, with its tendency to form the tibio-tarsus, the 

 avian phylum may have been given off from the 

 dinosaurian. This form of the Husleyau hypothesis seems 

 more probable than that the avian "phylum should have 

 originated quite independently from" a quadrupedal 

 proganosaurian [prosaurian] reptile, because the numerous 

 parallelisms and resemblances in dinosaur and bird 

 structure, while quite independently evolved, could thus 

 be traced back to a potentially similar inheritance." 



Although to the lay reader his mode of expression may 

 appear somewhat unnecessarily technical and abstruse, if 

 not, indeed, in certain respects, absolutely cryptic, there is 

 no doubt from the foregoing observations that Prof. 

 Osborn inclines to the belief that birds are in some 

 manner genetically connected with the dinosaurian reptiles, 

 although, from the existence of fully differentiated birds 

 at such an early epoch as the upper "Jurassic, the date of 

 divergence must have been extremely remote, possibly as 

 far back as the Permian. 



Before leaving this portion of the subject, a word is 

 advisable with regard to the flightless birds of the ostrich 

 group. Not very many years ago it was considered that 



* American Naturalist, October, 1900. 



this group was the oldest and the one nearest akin to the 

 extinct dinosaurs. It is now, however, quite evident, if 

 only from the structure of their degenerate wings, that 

 the ostrich-like birds, in place of being their ancestors, are 

 themselves descended from forms endowed with the power 

 of flight — whether from more than a single group we need 

 not now pause to enquire. It is true that in certain 

 respects their skeletons come nearer to the dinosaurian 

 type than is the case with those of their flying relatives. 

 But their resemblance — either by parallelism in develop- 

 ment, or by reversion to the common ancestral type — may 

 probably be explained by their mode of life being more 

 like that of dinosaurs, and perhaps in part by the large 

 bodily size of the majority of the group. 

 (Id he co)i!iiiued.) 



h 



LORD KELVIN'S NEW IDEA ABOUT ETHER 

 ATOMS. 



By Dr. J. G. McPherson, f.e.s.e. 



Lord Kelvin, President of the Royal Society of Edin- 

 burgh, startled the Fellows, on the evening of the 19th 

 January, with his new idea about ether atoms, in his 

 exposition of the reflection and refraction of light. He 

 lias hieen for years met by serious difficulties in carrying 

 out the practical conclusions of the undulatory theory of 

 light ; and these difficulties he exposed in detail. 



One investigator after another he found to make in- 

 genious suggestions on the old lines. But Fresnel, Green, 

 Voight and others, with all their ingenuity, could not 

 account for certain discrepancies. But Lord Kelvin, with 

 a master hand, has dispelled all these difficulties by a direct 

 denial of a tenet of the Schoolmen that " two bodies cannot 

 occupy the same space at the same time." Paradoxical 

 as it appeal's, he assumes the opposite, that two bodies 

 can occupy the same space. That is his main and funda- 

 mental tenet, and by it he is able to clear the air of what, 

 for a quarter of a ceutury, has interfered with his coming 

 to satisfactory conclusions on light and electricity. 



Leucretius was right in saying, two thousand years ago,' 

 that matter was not infinitely divisible, but that atoms 

 and the void constituted matter. These atoms, he con- 

 sidered, were indivisible, originally moving in parallel ( ^ 

 lines. His fallacy was in assuming that an atom had the y^ ^ 

 inherent /acH^ of changing the direction of its motion, so S§ 



that, by interrupting the parallel lines of motion of the"' 

 atoms by the alteration of direction at some point, atoms „ ?-L 

 were brought together out of the void to form matter. • yC 

 Tet Leucretius did not dream with his fallacy ; for Lord-y s 

 Kelvin, though discarding any idea of the quasi-living^xj V • 

 j)ower of the atom to change the direction of its motion, » ' X 

 assumes that there is an elecfrloii, or electric atom within "7 ^ 

 the material atom. '^ .C* 



Lord Kelvin assumes that, prima facie, according to the pj"^ 

 laws of dynamics, the material atom is of a spherical form. •.» 

 But this atom is permeated by the ether atom, both 

 occupying the same space. Though the electrion is not 

 material, the ether atom is material, of the fine jelly . ^ 

 constituency, infinitely incompressible, though easily ^t. rft 

 changeable in form. ^ i' 



He illustrated the combination of the ether andC/' ^ 

 ordinary material atoms in one spherical form and plac»>I. i ^'^ 

 bv simple experiments. If a piece of common shoemaker's"^ * - 

 rosin be hung in water, and an iron bullet be placed on^ J 

 the toj» surface of the hard rosin, the bullet will, throughX /* 

 time, slip inside the rosin. If, again, a spherical piece ot .^ 

 cork be placed under the rosin, it will work its way iJp 

 into the rosin, just as the iron bullet ivi-ought its, way 

 down. 



^ yf 





^mm^m^O^ «« 



