126 



NATURE 



[June 8, 1893 



LETTERS TO THE EDITOR. 



[ Tht Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.^ 



Mr. H. O. Forbes's Discoveries in the Chatham 

 Islands. 



In reply to Prof. Newton's letter, under the above title, in 

 Nature of last week (p. loi), in which he refers to the descrip- 

 tion by me of the Chatham Island Ralline bones under a distinct 

 genus Diaphorapteryx, and observes "that one thing seems 

 needed to make the discussion [on the probability of a land 

 connection between the Chatham and Mascarene Islands] real, 

 and tliat is the proof of the assertion that Aphanapleryx ever 

 inhabited the Chatham Islands," I beg to say that in his letter 

 there is a slight confusion of dates, which affects the question of 

 the nomenclature. On July 29 last year I visited Cam- 

 bridge for the purpose of comparing the bones from the 

 Chatham Islands I had brought with me with the real 

 Aphanapteryx remains in the Museum there. It turned out 

 that Dr. Gadow, who was abroad, had laid them aside 

 where Prof. Newton could not place his hand upon them, 

 and I was, therefore, unable to see them. A week or two later, 

 when in Edinburgh at the British Association Meeting, in a 

 note intimating the return of Dr. Gadow, and kindly arranging 

 for my examination of the bones. Prof. Newton adds, " I be- 

 lieve you will want a new generic name for what you have 

 called Aphanapteryx " and ?,\x^^i%\.%\hsmxa& Diaphorapteryx 

 instead. I was unavoidably long prevented from revisiting the 

 Cambridge Museum, and so in describing as Diaphorapteryx 

 the Chatham Island bones, at a meeting ol the British Ornitho- 

 logists' Club in December, 1892, I accepted the suggestion of 

 Prof. Newton, who alone had till then seen the remains from 

 both localities. On February 23, prior to reading my paper 

 at the Royal Geographical Society, I again visited Cam- 

 bridge, and in the most kind manner received every 

 facility and assistance both from the Professor and 

 from Dr. Gadow in comparing the specimens. On this 

 occasion I was unable to recognise any sufficient characters, 

 by which, in my estimation, to separate generically the bones 

 from the Chatham Islands from those from Mauritius. This 

 decision I stated at the meeting of the R.G.S. on March 13 last, 

 and more recently in a communication to the Brit. Ornith. Club, 

 which will appear in its forthcoming Bulletin. If I mistake not, 

 however. Prof. Newton agreed with me that the Chatham Island 

 form was nearer to Aphanapteryx than the latter wa? to Eryth- 

 romachus of Rodriguez. Some of these remains from Mauritius 

 have been figured by Prof. Milne-Edwards in his " Oiseaux 

 Fossiles de France," and the remainder are lully discussed and 

 illustrated by Dr. Gadow in a shortly-to-be-issued fasciculus of 

 the Trans. Z.S. of London, while those from the Chatham Islands 

 will appear shortly, I hope, in one or other of the scientific 

 journals or Proceedings. After a careful study of all the material 

 I have no hesitation, however, in stating meantime — as those 

 who care will then have an opportunity of judging — that the 

 bones from both regions are generically the same. I maintain also, 

 that even if some osteologists should be disposed (from the 

 somewhat larger size of the Chatham Island bones, though among 

 them I found a number scarcely to be separated on even that 

 ground) to make a generic distinction between them, the question 

 would not only not fall, but I really cannot see that the argument 

 based on their discovery in the New Zealand region would be in the 

 least invalidated, as the forms are unquestionably so very nearly 

 related. The importance of the distribution of the blue Water- 

 hens, and the relationship between the Huias of New 

 Zealand and the Frigelupus of Reunion — ^long ago pointed out 

 by Mr. Wallace— and many other facts as far as birds are con- 

 cerned recently urged by Dr. Sharpe at the Royal Institution, 

 appears now to a fuller extent by the discovery of those un- 

 expected forms in the Chatham Islands. 



1 must once more protest against the very erroneous state- 

 ment that I have invoked this "tremendous hypothesis " to 

 explain the distribution of the closely related forms of these 

 two regions. I adduced, as I have said in my last letter, a 

 great deal of other evidence in my paper at the Royal 

 Geographical Society, which will appear very soon now. 

 In addition to the facts there given I may point out the sig- 



NO. 1232, VOL. 48] 



nificance to this question of the results of the investigations of 

 my lamented friend, Mr. W. A. Forbes — an anatomist of the 

 highest acumen — on the genera Xenicus and Acanthisitta of 

 New Zealand. He found that the affinities of the Xenicida: are 

 with the Pipridce (including the Cotingida), Tyrannidn, 

 Pittida, and Phitepittida: — groups confined to the New Zealand, 

 the Australian (ranging into the Oriental), the Mascarene, and 

 the Neotropical regions, and that they have no relatives else- 

 where. Nor are the following sentences from Mr. Wallace's 

 ' ' Geographical Distribution of Animals " without a bearingon this 

 discussion : — " We have the pigeons and the parrots most 

 wonderfully developed in the Australian region, which is pre- 

 eminently insular, and both these groups have acquired 

 conspicuous colours very unusual or altogether absent elsewhere. 

 Similar colours [black and red] appear in the same two groups 

 in the distant Mascarene islands. . . . Crests, too, are largely 

 developed in both these groups in the Australian region only ; 

 and a crested parrot formerly lived in Mauritius — a coincidence 

 too much like that of the colours as above noted, to be con- 

 sidered accidental." KenRy O. Forbes. 

 104, Philbeach Gardens, Earl's Court, S. W. 



The Fundamental Axioms of Dynamics. 



As Prof. Lodge refei-s in the letter published in this week's 

 Nature, p. loi , to my remarks on his paper on the Fundamenta I 

 Axiom of Dynamics, I shall be obliged if you will allow me ti> 

 state my views in your columns. Apart from all minor questions 

 it appears to me that the main issue raised by Prof. Lodge is 

 whether the law of the conservation of energy can \>s proved Wou\ 

 the fundamental laws of dynamics and the assumption of contact 

 action. 



I have not the slightest objection (as he seems to suppose) to 

 the mathematical investigation of physical facts being based on 

 assumptions which are followed out to their logical conclusions, 

 nor do I shrink from using such methods even when they fail in 

 some points or lead to paradoxical conclusions. They may 

 legitimately be accepted as convenient though imperfect mental 

 pictures of the truth, sketches, but not finished drawings. 



My objection to Prof. Lodge's "proof" is that in his attempt 

 to avoid the unthinkable by discarding action at a distance, he 

 adopts another equally inconceivable conception, viz. contact 

 action. 



He has already laid it down as|an axiom that "material particle; 

 (atoms of matter) never come into contact." It is only by 

 abstaining from the attempt to define the constitution of the 

 ether that he avoids being driven to the conclusion that its 

 various parts never come into contact either. 



The assumption that he really makes is that when two bodies 

 (including in that term both matter and the ether) act immediately 

 upon each other, the distance between the mutually acting 

 parts remains invariable during the action. This is not incon 

 sistent with action at a distance. If then the phrase "contact 

 action " be discarded the assumption of action at constant dis- 

 tance is a proper subject for investigation. 



If the assumption be accepted the reasoning based on it is 

 no doubt correct, but the value of the " proof" (regarded as 

 independent or self-contained) depends entirely on the value we 

 assign a priori to the fundamental assumption. I doubt whether 

 an argument based upon it would by itself have convinced the 

 world that the conservation of energy is a fact. 



If, on the other hand, the assumption is regarded as a more 

 or less arbitrary postulate to be justified, ii posteriori by the fact 

 that conclusions can be deduced from it which _are otherwise 

 known to be true. Prof. Lodge must not represent his course as 

 the ascent of a firm ladder of argument to results which, though 

 paradoxical, must be accepted under penalty of a reductio ail 

 absurdum. On the contrary, it lies with him to justify his 

 assumption by the use he makes of it. That the conservation 

 of energy follows is no doubt an argument in its favour, and I 

 for one shall look with interest for the other deductions which 

 Prof. Lodge promises. Arthur W. Ri cker. 



June 2. 



If Mr. E. T. Dixon (Nature, p. 103) will read what I have 

 previously written on the subject of energy he will find most of 

 his objections anticipated. I have pointed out, as he now does, 

 that no long as potential energy is regarded solely as a "force 

 function" the conservation of energy has no real physical mean- 

 ing (PP- 532, 533. Phil. Mag., June 1881). I quite agree that 

 potential energy belongs to a system rather than to a particle. 



