Maech 2, 1891.] 



KNOWLEDGE. 



43 



southern hemisphere that on a bright moonhght night, 

 when the fainter hicid stars are invisible, the position of 

 the Millcy Way can be traced by the condensation of the 

 brighter stars alone along its course. Now, there is no 

 antecedent reason why the naked-eye stars should collect 

 upon one part of the Milky Way and not upon another ; 

 and hence there is no reason why the fainter parts of the 

 galaxy — assuming them for the moment to be the most 

 distant — should not have collected fourth and fifth mag- 

 nit ade stars in the same way as the brighter and (there- 

 fore assinned) nearer parts have collected the brighter 

 magnitudes. But we should not expect to find many of 

 the brightest stars on the fainter and more distant parts. 

 Yet it is a fact that there are stars on the (assumed) more 

 distant streams, and obviously associated with them, as 

 bright as those on the (assumed) nearer ones. Moreover, 

 between the two streams, where the Milky Way is double, 

 and in the Coal-sacks, scarcely a single lucid star is to be 

 seen. This is a singular circumstance. If the spiral 

 theory, or any modification of it as suggested by Proctor, 

 were true, we shoidd expect more, or at least as many, 

 bright stars between the two branches where the Milky Way 

 is double, and in the Coal-sacks, as upon the borders of 

 the Milky Way in any other place. On the other hand, if 

 we regard the two branches as lying at very nearly the 

 same distance from the Sun, we can see at once that the 

 cause which separated them, or keeps them apart — what- 

 ever the agency may be scarcely matters in this inquiry — 

 would also ih-i-dn, as it were, the lucid stars from the space 

 between. Add to this the circumstance that the meander- 

 ings of one branch correspond to those of the other, and 

 that in one place one branch is made up of alternating 

 bright and faint patches corresponding to faint and 

 bright patches respectively on the other, then we have 

 strong presumptive evidence that the two branches 

 are closer together than any spiral conformation would 

 admit. 



All this leads us to conclude that the Milky Way is 

 much as it seems to be at first, namely, a very complex 

 stream of stars roughly hoop-like, and not spiral-like, in 

 form. A piece of old rope thrown into a circular shape 

 represents the Milky Way very well. The frayed ends 

 not quite meeting represent the fan-shaped expansions of 

 the stream on each side of the rift in Argo (a spiral theory 

 does not explain why these expansions should occur just 

 here). A strand untwisted of nearly half the length of 

 the rope, and divided in the middle, would represent the 

 divided branch running from Cyguus through Ophiuchus 

 and Scorpio. Smaller departures would represent the 

 lateral extensions in Cepheus and Perseus. These may be 

 of any size ; and it scarcely needs Proctor's assumption 

 that a vast void separates the galactic stars fi'om the faint 

 streams discovered by Sir .John Herschcl to account for 

 them. This faintness is very likely caused either by 

 sparcity of distribution or by the smallness of the stars 

 (as we have seen brightness is no test of distance so long 

 as light is not lost in its passage through space) ; indeed, 

 it is pretty clear that the Milky Way is made up of stars 

 of all orders of size and brightness. Local unravellings 

 in the rope would correspond to the Coal-sacks in Crux 

 and Cygnus, and to the lacunre in Scorpio and else- 

 where. 



In conclusion, let me add that the aspect of the Milky 

 Way in Argo gives a very strong impression that the stream 

 has been forcibly torn asunder at this place, an impression 

 which is to some extent corroborated by the positions of the 

 bright stars round about, and by the numifold signs of 

 decomposition exhibited l)y the galaxy in Scorpio and the 

 adjacent constellations. 



GIANT BIRDS. 



By R. Lydekker, B.A.Cantab. 



THE only birds existing at the present day which 

 in any sense merit the epithet "gigantic" are the 

 Ostriches of Africa and Arabia, the Eheas of 

 South America, the Cassowaries of Papua and 

 North Australia, and the Australian Emus ; and 

 even the largest of these — the male Ostrich — seldom ex- 

 ceeds seven feet in height. The researches of palicontolo- 

 gists have, however, revealed to us that these four groups 

 are but the solitary survivors of a considerably more 

 extensive assemblage of Criant Birds which was once 

 spread over a large portion of the globe, and some of 

 whose members as much surpassed the Ostrich in size as 

 the latter exceeds the Eheas in this respect. Indeed, 

 with our present knowledge of the meaning of the 

 geographical distribution of animals, the very circum- 

 stance that the existing Ciiant Birds are all more or less 

 closely allied, and are fovmd scattered over the globe in 

 areas widely separated and totally disconnected from one 

 another, would of itself have been amply sufficient to 

 indicate that they are the remnants of a group which was 

 at one time of much larger extent, and inhabited regions 

 where such creatures are now unknown. It is unfortu- 

 nately the case that there are still many gaps in the chain 

 which should link all the existing Giant Birds together, 

 but we may confidently hope that the progress of geo- 

 logical research will little by little reduce the number and 

 length of these gaps. 



All the Giant Birds, it may be observed, both living and 

 extinct, are linked together by their incapacity of fiight, 

 and the consequent absence of that strong bony ridge or 

 keel which we may observe on the breast-bone of a duck 

 or a fowl, and the presence of which is essential to form 

 a firm support for the powerful muscles requked to move 

 the wings. Whether, however, this incapacity for flight 

 is a feature which was always possessed by the Giant 

 Birds, or whether it has been gradually acquired by 

 disuse, is a question which has seriously exercised the 

 minds of those best fitted to decide it, and, since it is still 

 unanswered, may be put aside on this occasion. Moreover, 

 in saying that the Giant Birds are all incapable of fiight, 

 it must by no means be inferred that all birds in that con- 

 dition have any affinity to this group. On the contrary, 

 precisely the opposite is the case, since in the extinct 

 Dodo of the Mauritius we have an instance of a huge 

 pigeon which had evidently lost the power of flight ; and 

 the superficial deposits of New Zealand have yielded the 

 remains of a large rail and a goose which were in the 

 same predicament. These and other flightless birds difler, 

 however, essentially in several parts of their organiza- 

 tion from the true Giant Birds, and thus have no sort of 

 connection with the subject of this article. There are, 

 however, certam birds, namely the little Kiwis of New 

 Zealand, which, although by no means entitled to rank as 

 Giant Birds in the proper sense of that term, yet as 

 being closely related to the typical members of that group, 

 must find a place therein. 15efore, however, we can 

 consider the fossil members of this group it is necessary 

 that we should have some idea of the general structure of 

 the leg of a bird, since it is this part of the skeleton 

 which is most commonly met with in a fossil eoudition, 

 and which aftbrds the most important clue as to the size 

 and affinities of the bird to which it belonged. Some 

 observations on this point have already been made in the 

 article on Giaiit Keptiles ; but since those observations 

 were mainly directed to showing the resemblance between 



