NATURE 



\Nov. 5, 1874 



British Islands and the more temperate parts of Europe it is very 

 possibly only the young of this species which migrate, and the 

 adults, liaving once fixed on_a place of residence, may stick to it ; 

 so that here we have a case which will almost bear out Mr. 

 Wallace's supposition. With this, however, he stops, and I am 

 sorry to say offers no suggestion as to the way in which migration 

 is effected. 



The question which Mr. Romanes puts would be more ap- 

 propriately answered by Mr. Tegetmeier, and I hope he will be 

 niduced to do so. I can only say that that gentleman has 

 repeatedly urged his views on me in conversation and upon the 

 public in his books (see " Pigeons, their Structure," &c., pp. 

 S4, 85, and " Tlie Homing or Carrier Pigeon," pp.37 — 42, 

 105 —118) which, being ready of access, I need not here quote. 

 To limit myself to what I am alone answerable for, I would say 

 that when declaring that sight alone cannot be much aid to birds 

 while migrating, I had especially in mind the almost peculiar case 

 of the Scandinavian form of lilucthroat (Ruliiilla siiniia), whicli 

 winters in Egypt and the Nile Valley.and summers in the northern 

 or mountainous parts of Sweden, Norway, Finland, and I'iussia ; 

 while, though no doubt passing regularly twice a year over the 

 intervening countries of Europe, it is lliere so singularly scarce 

 as to have been, until of late years, almost unknown to the best 

 of German ornitliologists. For the benefit of such of my 

 readers as are unacquainted with the bird, I may add tliat the 

 cock has a conspicuous and beautiful plumage, a fine song, and 

 habits which, in the spring of the year, cannot be called unoh- 

 trusive. If, therefore, it did commonly occur in Germany — 

 where I should state that a kindred form {Riilicilla IciUivyana) 

 is very well known — it could not escape observation. Won- 

 derful as the feat looks, it would therefore seem as though this 

 Scandinavian Bluethroat passed over Europe at a stretch, and if 

 so, I cannot conceive its flight being guided by any landmarks. 



Furthermore, there is ground for believing that some of the 

 migrations of many species, particularly of water-birds, are 

 performed at night, when sight, one would think, can be of 

 little use to them. But, to be honesl, I must confess that dark, 

 cloudy nights seem to disconcert the travellers. On such nights 

 the attention of others besides myself has often been directed to 

 the cries of a mixed multitude of birds hovering over this and 

 other towns, apparently at a loss whither to proceed, and attracted 

 liy the light of the street-lamps. 



One other point only need I now mention ; this is Mr. 

 Romanes's assertion that "in the case of all migratory birds, 

 the younger generations Hy in company with the older ones," 

 which is at variance with a statement (hitherto, I believe, un- 

 controverted) of Temminck's : — " On peut pour un fait que les 

 jeunes et les vieux voyagent toujours separement, le plus souvent 

 par les routes differentes." (Man. d'Orn. ed. 2, iii. Introduc- 

 tion, p. xliii. note.) Alfred Nicwton 



Magdalene College, Cambridge, Nov. 2 



Insects and the Colours of Flowers 

 There is one point connected with Mr. Darwin's explanation 

 of the bright colours of flowers which I have never seen referred 

 to. The assumed attractiveness of bright colours to insects 

 would appear to involve the supposition that the colour-vision of 

 insects is approximately the same as our own. Surely this is a 

 good deal to take for granted, when it is known that even among 

 ourselves colour-vision varies greatly, and that no inconsiderable 

 number of persons exist to whom, for example, the red of the 

 scarlet geranium is no bright colour at all, but almost a match 

 with the leaves. R.vyleigh 



Whiltinghame, Preston Kirk 



Sounding and Sensitive Flames 

 A SE^■ERE indisposition, which disabled me from correspon- 

 dence during nearly the whole of last month, prevented me from 

 acknowledging as soon as it appeared in Natiire (vol. x. p. 244) 

 Prof. Barrett's excellent communication on Sounding and Sensitive 

 Flames, replying to my letter on the same subject at page 233 of 

 this volume. Prof. Barrett supplied me with many useful references, 

 and with one at least the want of which led me to misrepresent 

 his connection with the discovery of sensitive properties in suit- 

 ably adjusted wire-gauze flames, for which I had sought in 

 magazines and journals for some months previously in vain. A 

 note of the original description of Mr. Barry's experiment in 

 N.-\.TURE, vol. v. p. 30, had in the meantime been pointed out to 



me in another record of very similar experiments, which is itself 

 also, I have no doubt, the same account of "further expe- 

 riments with the same kind of tlame," that Prof. Barrett cites as 

 appearing in the Joiinial of the fiaii/diii Iiisliliite for April 1872, 

 to which I have not been able to obtain access. The nearer channel 

 to which I was referred for its perusal is the Pliilosoplncal Maga- 

 c/hi' for June 1872, where a paper is briefly extracted from the Ame- 

 rica}! Journa/ of Scieiice of the preceding month, describing new 

 experiments with Barry's sensitive flame, by Mr. \V. E. Geyer, 

 of the Stevens Institute ot Technology, in the United States. 

 By placing a wide tube over the ilame at a proper height 

 it became sounding, or, if silent, might be made sensitive in 

 such a way as to sound at the slightest hiss or rustle, and on 

 producing any jingling or tinkling sounds in its neighbourhood. 

 Thus the flame sounded twice on pronouncing to it the word 

 "sensitive," showing its instantaneous aftection even by mo- 

 mentary sibilant sounds. By varying the experiment, an oppo- 

 site condition of the flame was obtained, in wliich it continued 

 sounding until checked by a hiss or rustle from without. It is 

 observed by the editor of the American Journal of Scienee, in a 

 note to Mr. Geyer's paper, that in the number for September 

 1S71, of the Atoiiileur Scieiilifupie, a form of apparatus and 

 experiment apparently identical with Mr. Barry's is noticed as 

 having been made by Prof. Govi at Turin, and this was a few 

 months prior to the letter in which the account of his experi- 

 ments is given by Mr. Barry to Prof. Tyndall. Thus the sen- 

 sitive properties of certain wire-gauze flames, like the property 

 of such flames to excite very readily musical vibrations, may have 

 had many independent discoverers ; the value of such dis- 

 coveries is now, as it must have ever been, the new light which 

 one is capable of throwing upon another. The rapid publication 

 of results urgently requires their frequent collection and com- 

 parison together ; and this process, pressing and urgent as it is, 

 seldom fails in experienced hands to prove a connection, to 

 bind together a chain of consequences, and to leave a subject 

 in general better explored and embellished with new-found illus- 

 trations than it was before. Such was the successful treat- 

 ment, a few years ago, by Prof. Tyndall, of the question of 

 sounding and sensitive flames, when it was shown by beautiful 

 illustrations of Savart's sensitive water-jets, and by equally 

 ingenious and new experiments with smoke-jets as substitutes 

 for flames, that sensitiveness is a residing property of liquid 

 veins and gasjets, independently, in the latter case, of their 

 being lighted. The laws of fluid pressure and motion, and 

 apparently foremost of all those of capillary attraction in liquids 

 ind of mutual friction and diffusion in gases, and not the 

 energies of heat and combustion of a flame, preside prin- 

 cipally over the observed phenomena. The bifurcated head, or 

 low ruffled brush to which the tall wand-like sensitive jet is 

 suddenly reduced, is but the glowing representation of the form 

 which, if it were visible to the eye, the unlighted jet would, 

 under the same circumstances, be observed to take. This is at 

 least in general terms, and perhaps also in plain and fairly accurate 

 statement of the real facts, the simple result which the collection 

 and elucidation of the most brilliant then known experiments 

 illustrating sensitive flames, led a philosopher of Prof. Tyndall's 

 enlightened sagacity and skill in physical investigations to adopt. 

 There can be no doubt of its subst.antinl correctness in the in- 

 creasing array of cases to which it may be successfully applied. 

 The flame is but an illuminated effigy of some of the lowest parts 

 of the issuing gas column, whether tranquil or disturbed, whose 

 upper parts it removes and replaces by products of combustion. 

 The lower parts are also marred in their form by heat, but not 

 so much as to obliterate the original character, shape, and 

 dimensions of the part of the gas column that it represents. 

 The flame terminates upwards, and ceases to represent the 

 unlighted column further when it has found surface of contact 

 enough with the outer air to effect the complete com- 

 bustion of the gas. The up-draught of violently heated 

 products of combustion near the base impedes the access of 

 fresh air to parts near the summit of the flame, and it must, 

 besides, deform them otherwise, sometimes even rhythmically, 

 as in the unsteady throbbing flame of an ill-trimmed lamp 

 or of a candle burning in its socket. The noisy roar with which 

 flaring of gas-flames is attended tells us also of the uneven mix- 

 ture of the gas and air supplies with each other in the flame, 

 and reminds us of the rapid fire of small explosions that must 

 probably introduce new sources of confusion in its form. If 

 those explosions, however, are regularly timed, they can be 

 made to maintain the simple musical note of harmonic flames ; 

 and these flames again, wholly dependent as they appear to be 



