April 2/^, 1S79] 



NATURE 



579 



pages, and contains merely a iev/ illustrations of the 

 capacity inherent in music of modulating the pleasant 

 sensation it produces in the mind of man in a number of 

 various ways. An appendix treats of the pleasure man 

 derives from the aspect of colours, certain forms, and the 

 beauty of the human body. 



LETTERS TO THE EDITOR 



{The Editor does not hold h imself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, or 

 to correspond with the writers of, rejected manuscripts. No 

 notice is taken of anonymous communications. 



[The Editor urgently requests correspondents to keep their letters as 

 short as possible. The pressure on his space is so great that it 

 is impossible othenvise to ensure the appearance even of com- 

 munications containing interesting and noz^el facts."] 



On the Spectrum of Brorsen's Comet 



The observations of Prof. Young on the present appearance 

 of the spectrum of Brorsen's comet are of great interest, from 

 the circumstance to which he refers in his letter in Nature, 

 vol. xix. p, 559, namely, that in 1868 I found the positions of 

 the three bright bands of this comet not to agree with those of 

 other comets which I showed to be coincident with the bright 

 bands in the spectrum of flames containing carbon. 



The care I bestowed upon the determination of the apparently 

 anomalous character of the spectrum of Brorsen's comet in 1868 

 gives me great confidence in its approximate accuracy. I wish 

 now to call attention to the fact that a spectrum apparently 

 essentially similar to the peculiar one exhibited by Brorsen's 

 comet in 1868, was observed at Dunecht by Lord Lindsay in 

 the case of Comet C 1877 (Borelly's). It is remarl<able that 

 another comet, Comet B (Winnecke's) 1877, observed by Lord 

 Lindsay on the same evening (May 6) presented the ordinary 

 cometary spectrum. 



Lord Lindsay's diagram in the Monthly Notices R.A.S. (vol. 

 xxxvii. p. 431) of these two spectra agrees as nearly as can be 

 expected in such observations with my diagram in the Phil. 

 Trans., i868 (PI. xxxiii.), contrasting the spectrum of Comet B, 

 1868, with that of Brorsen's comet. 



It may be accepted, therefore, as beyond doubt that the un- 

 usual form of spectrum of Brorsen's comet in 1868 is occasion- 

 ally presented by comets. The great interest of Prof. Young's 

 observation lies in the information which it gives us that the 

 same comet may present on one occasion one spectrum, and on 

 another the other spectrum, 



I regret that the special arrangement of my telescope for pho- 

 tographic work does not permit me to observe the spectrum of 

 Brorsen's comet at its present appearance. 



Upper Tulse Hill William Huggins 



The Migration of Birds 



In Nature, vol. xix. p. 433, there is a notice of my paper 

 " Ueber das Wandern der Vogel," to which I have somewhat to 

 reply. 



However agreeable it is to me that my views should be com- 

 municated to your readers, and however little I object to their 

 being submitted to rigorous criticism, I must still also desire that 

 this criticism be fair. 



I believe it is due to differences of national customs that your 

 reviewer has not quite satisfied this desire. We make, perhaps, 

 in Germany a sharper distinction between a scientific treatise and 

 A popular \,oxV. than in England. Of the latter we do not re- 

 quire that it bring forth what is new, but only that it should give 

 what it has to give in a clear and easily intelligible manner. Nor 

 do we require completeness of such a work, or even a criticism 

 of the scientific works on which it is based ; indeed, it is gene- 

 rally left to the author how far to cite his sources of information 

 »nd how far not. In the scientific treatise it is quite otherwise ; 

 here only that is of value which is new ; the theme must be 

 treated exhaustively ; the sources must always be named and 

 dealt with critically, &c. 



Now my publication is a lecture, which was delivered before a 

 company of educated ladies and gentlemen, and so before mere laics, 

 Md a year and a half afterwards was printed in Virchow and 

 Holtzendorff's Collection of Popular Lectures. It thus belongs 

 unquestionably to the categorv of popular writings. 



For this reason your severe critic had no occasion to point out 

 that in my lecture there is much that had been long known, that 

 sources are named but rarely, and that no scientific criticism is 

 exercised. That is quite a matter of course in a popular work, 

 at least in Germany. Mr. Newton would have had much better 

 right to feel surprised that even any new ideas were contained 

 in it. 



My original aim in this lecture was merely to make my hearers 

 acquainted with the new facts and views on the migration of 

 birds, as they have been established by Wallace, Middendorff, 

 and especially by Palmen. As I followed the new facts theo- 

 retically to their consequences, there arose perhaps some new 

 ideas, which I should be glad to find verified in the future. 



It is further a matter of course that, notwithstanding the 

 popular form of my work, I stand by all that I have said ; but I 

 must protest against being made responsible for what I have not 

 said! 



Thus, e.g., I have nowhere said that I hold Palmen's routes of 

 flight for "absolute truths." I am rather quite of Mr. Newton's 

 opinion, that these routes are merely inferred, not directly ob- 

 served, and therefore that they are to a certain extent "conjec- 

 tural." In this sense, however, the routes of birds must ever 

 remain comparatively "conjectural," unless one were to follow 

 the birds in a balloon. But while "conjectural," Palmen's 

 routes are yet inferred by a purely scientific method, and I doubt 

 not that most of them will in the main be confirmed by further 

 observations. Precisely in the application of this method lies 

 Palmen's great merit, and it is only to be hoped that ornitho- 

 logists w ill follow further in his footsteps, and correct his mis- 

 takes by accumulation of new facts. That Palmen's routes con- 

 tain some errors I do not doubt ; I should rather wonder if it 

 were not so. 



Little, however, comes of this with reference to the questions 

 which are treated with special fulness in my lecture, the origina- 

 tion of the instinct of migration, and the powers by which the bird 

 reaches its distant goal. 



I have, further, nowhere said that birds fly over the sea at a 

 height of 20, coo feet, but have merely cited the fact that birds 

 have been seen at such height ; with reference, of course, to ex- 

 planation of their flight over the sea, I believe that birds, in 

 flight over the sea, do not close their eyes, but exercise their keen 

 eyesight as far as possible. Therew ith, however, it is not said 

 (as Mr. Newton imputes to me) that in all flights over the sea 

 they always keep the land in sight. 



I desist from adducing further misunderstandings by Mr. 

 Newton, and come to what / have actually said and am minded 

 to maintain. 



In agreement with Palmen, I have expressed the opinion, that 

 migratory birds have no special sixth sense, as Middendorff has 

 assumed, but that they find their way only with the help of their 

 cn-dittary five senses. 



Mr. New ton seems to be of a different opinion. He does not 

 say, indeed, whether he agrees with Middendorff, but he brings 

 forward observations which appear incapable of harmony with 

 my view. 



First, there appear in New Zealand two species of cuckoo 

 ( Chrysococcyx lucidus and Eudynamis taitensis) which regularly 

 fly some 1,000 miles' distance over the ocean. I believe with 

 Mr. Newton that the birds cannot fly so high as to see at once 

 New Zealand and the Norfolk or Kermadec Islands, though on 

 the former is a hill of i,oco feet. Likewise I will accept the 

 case of Charadrius pluvialis as a regular guest of the Bermuda 

 Islatids, and a doubtful Charadrius species as regular guest of 

 the Sandwich Islands. All these observations are, indeed, still 

 very imperfect, inasmuch as it is not known whence the birds 

 come nor whither they go ; but so much seems certain, that they 

 do regularly fly over large stretches of ocean in w hich are almost 

 no islands or rocks, and which are so great that they must of 

 course also fly by night. 



What then? Are we therefore compelled to make the 

 assumption, with Middendorff, of a sixth sense, which informs 

 the bird which direction is north ? Is there no simpler explana- 

 tion of the fact ? Obviously, we should only be warranted in 

 accepting such a purely hypothetical sense, if it were clearly 

 proved, that we could never get to understand the facts without 

 it. 



The question had already occupied me, before I knew of 

 Mr. Newton's examples. I omitted it in my lecture, because it 

 seemed to lead me further into the region of hypotheses than I 

 considered I could answer for before my audience. 



