354 



NATURE 



\Feb. 22, 1877 



harmonics and the scale are treated of, and I am not sur- 

 prised that its author cannot understand the numerical basis of 

 Cohn Brown's Just Intonation Harmonium. 



The strict harmonic chords of the seven notes of the scale, 

 including only sounds in the scale of C, and excluding all approxi- 

 mations, are these :— 



Here it will be observed that all the tones of the scale are 

 harmonics of F and of that note only (a circumstance first pointed 

 out by Colin Brown). I do not admit that F and A are notes 

 interposed in the scale of C. A. R. CLARKE 



Ordnance Survey Office, Southampton, February 8 



Protective Mimicry among Bats 

 I HAVE read with much interest the remarks of Dr. S. Archer 

 in Nature, vol. xv. p. 313, on the habits of Ryjichonycteris 

 naso, Wied. (= Proboscidea saxaiilis et rivalis, Spix. ), as they 

 quite agree with notes on the same species made by me when 

 travelling some years ago in British Guiana. 



This is not, however, the first published notice of protective 

 mimicry among bats. In my " Monograph of the Asiatic 

 Chiroptera" (1876), I have referred to the peculiar markings of 

 the wing and interfemoral membranes in Kenvoula picta, Vesper- 

 tilio formostis, and V. Welwilschii, which are coloured on the 

 same plan although these species are related in no other 

 respects, and have stated that I believe these markings to be the 

 result of "protective mimicry." Of one of the two first-named 

 species, Mr. Swinhoe remarks : — " A species of Kerivoida allied 

 to K. picta and K. forviosa, was brought to me by a na'ive. 

 The body of this bat was of an orange brown ; but the wings 

 were painted with orange-yellow and black. It was caught, 

 suspends d head downwards, on a cluster of the round fruit of the 

 Longan-tree {Nephelium lottganum). Now this tree is an ever- 

 green ; and all the year through some portion of its foliage is 

 undergoing decay, the particular leaves being, in such a stage, 

 partially orange and black. This bat can, therefore, at all 

 seasons, suspend from its branches, and elude its enemies by its 

 resemblar.ce to the leaf of the tree. It was in August when this 

 specimen was brought to me. It had at that season found the 

 fruit ripe and reddish-yellow, and had tried to escape observa- 

 tion in the semblance of its own tints to those of the fruit." ^ 



A familiar instance of what appears to be "protective 

 mimicry " occurs in the species of the genus Pteropus (Flying- 

 foxes of European residents in India). These, the largest of all 

 bats, measuring, on an average, nearly one foot in length with an 

 expanse of wing of from four to five feet, are, from their large 

 size, very conspicuous objects even when the wings are closed, 

 and easily seen from the ground when hanging from lofty trees. 

 With very few exceptions these bats have the lur of the back of 

 the head and of the nape of the neck and shoulders of a more or 

 less bright reddish or bright buflf colour, contrasting strongly 

 with the dark brown or black fur of the back. At first sight it 

 might appear that this remarkable contrast of colours would 

 render the animal more conspicuous to passing enemies, and con- 

 sequently more subject to their attacks when hanging in a semi- 

 torpid condition. But any one who has seen a colony of these 

 bats suspended from the branches of a banyan tree, or from a 

 silk cotton tiee (Eriodeftdron orientale), must have been struck 

 with their resemblance to large ripe fruits, and this is especially 

 noticeable when they hang in clusters from the leaf-stalks of the 

 cocoa-nut palm, where they may be easily mistaken for a bunch 

 of ripe cocoa-nuts. Hanging close together, each with his head 

 bent forwards on the chest, his body wrapped up in the ample 

 folds of the large wings, and the back turned outwards, the 

 ' Proc. Zool. Soc, 1862, p. 357. 



brightly coloured head and neck is presented to view, and re- 

 sembles the extremity of a ripe cocoa-nut, with which this animal 

 also closely corresponds in size.-^ 



The much smaller species of Cynopterus and Macroglossus, 

 which feed on the fruit of guavas, plantains, and mangoes, re- 

 semble these fruits closely in the yellow colour of their fur and in 

 their size, so that it is very difficult to detect one of these bats 

 when suspended among the leaves of any of these trees. 



The resemblances, however, between these frugivorous bats 

 and the fruits of the trees on which they roost, may be acci- 

 dental, and, in the present state of our knowledge, we would 

 scarcely be justified in setting them down as the result of "pro- 

 tective mimicry," though there can be little doubt that, to what- 

 ever cause due, they aid in concealing these animals from the 

 attacks of enemies. 



I could adduce other instances of what appear to me to be 

 cases of "protective mimicry" among bats, but my letter has 

 already much exceeded the limits intended by me when I com- 

 menced it, and I must reserve my remarks on the peculiar posi- 

 tion of Rynchonyctens naso when resting on a perpendicular 

 plane surface for another communication. G. E. D©KSO^f 



Sense of Hearing in Birds and Insects 



In respect to "The Sense of Hearing in Birds," the habit 

 of pattering with the feet while seeking food, which is common 

 to many worm-eating birds, seems to preclude the idea that such 

 birds at least depend to any great extent upon their powers of 

 hearing. Gulls frequently tread or patter with their feet while 

 seeking food. The object being clearly to discover, from some 

 slight movement, the whereabouts of their hidden prey. Plovers, 

 doubtless with the same object, vibrate one loot rapidly with 

 tremulous motion on the ground. Now the plover is essentially 

 a worm-catching bird, more so even, probably, than the thrush. 

 Light-footed, active yet stealthy in its movements, quick-sighted, 

 and certainly quick of hearing, the plover, when feeding, runs a 

 little way, hke the thrush, then stops, with head erect, looking 

 intently ; listening it might well be thought but for the tremulous 

 motion of its foot. The plover, at such time, trusts without doubt 

 to sight and not to its sense of hearing. 



It is true that the thrush has not this trick of pattering with 

 the foot. It is true also that it has, while seeking food, very 

 much the look of listening attentively. The largeness of its eye 

 and comparatively small development of its ear incline me, how- 

 ever, to believe with Mr. McLachlan (Nature, vol. xv. p. 254), 

 that the thrush also depends when feeding more on its power of 

 sight than on its sense of hearing. C. J. A. Meyer 



THE ATMOSPHERE OF THE ROCKY 

 MOUNTAINS^ 

 A NYONE who observes with a large telescope soon becomes 

 ■^"^ aware of the great obstacle atmospheric undulation offers 

 to the pursuit of astronomy, particularly in the application of 

 photography and the spectroscope. During two years when I 

 photographed the moon on every moonlight night at my obser- 

 vatory,^ there were only three occasions on which the air was 

 still enough to give good results, and even then there was un- 

 steadiness. Out of 1,500 lunar negatives, only one or two 

 were really fine pictures. A letter which the late Mr. Eond 

 wrote to me states that in seventeen years he had never met 

 with a perfectly faultless night at the Cambridge Observatory. 



Such facts naturally cause astronomers to consider whether it 

 is not possible to diminish ^atmospheric disturbances, and have 

 led to the celebrated expeditions of Prof. Piazzi Smyth to the 

 Peak of Teneriffe, and Mr. Lassell to Malta. Theoretically it 

 would seem that the only complete solution is to ascend high! 

 mountain ranges or isolated peaks, and leave as much as possibW 

 of the air below the telescope. 1 



Having had occasion during the months of August and Sep/ 

 tember, 1876, to go on a hunting trip with two distinguished 

 officers of the United States Army into the Rocky Mountain) 



' In a note to Sir James Emmcrson Tennent's " Ceylon." Mr. Ihwaita 

 remarks : — " These bats {Pteropus mednis) take poshessioii during the d* 

 of particular trees, upon which they hang like so much ripe fruit." I 



'■' " Astronomical Observations on the Atmosphere of the Rocky Mouf' 

 tains, made at Elevations of from 4,500 to 11,000 feet, in Utah, Wyomic 

 Territory and Colorado." By Henry Draper, M.D., Professor of Analytiil 

 Chemistry and Physiology in the University of New York. Communicati 

 by the author. 



3 Prof. Henry Draper's observatory is at Hastingson-Hudson, near Nv 

 York ; latitude 40° 59' 25", longitude 73° 52' 25" ; elevation above the sea, : 

 feet. / '■ 



