‘from the 
do suck the blood of sleeping persons. 
412 
-SWATURE. >, 
de 
vampire bats as those which suck the blood of sleeping persons, 
whereas the truth is, as Belt has remarked, ‘the vampire is the 
most harmless of bats.’ ”’ 
In Charles Darwin’s ‘‘ Voyage of the Beagle,” we find an 
account of a vampire bat (Desmodus d'orbignyz) sucking the 
withers of horses during repose. We also have Charles Water- 
ton’s most circumstantial account of the sucking of the blood of 
human sleepers. Waterton says there are two species, only one 
of which attacks man. The Rev. J. G. Wood tells us in his 
notes to “‘ Waterton’s Wanderings” that the bat is Vampirus 
spectrum, on what authority he does not say, but quotes 
C. Kingsley in confirmation of the blood-sucking habit. Again, 
Prof. Mivart has an article in the Popular Science Review for 
July, 1876, on bats, in which he not only quotes Darwin’s 
account, but speaks of the modification of the teeth and stomach 
of Desmodus as specially suited to this habit. What I wish to 
ask in all humility, as a mere onlooker, is, How are we to 
reconcile the above statement with all this authority ? 
94, Jacob Street, Liverpool, February 12 A. W. AUDEN 
T INADVERTENTLY wrote the name of Belt while quoting 
work of Bates. The answer to the question 
which your correspondents ask is sufficiently simple, and 
has, in fact, been furnished by one of them, viz., that 
while the vampire bat itself does not suck blood, the name 
is popularly extended to other kinds of bats which do. These 
other kinds—or at any rate some of them—belong indeed to the 
‘same sub-family as the vampire (viz., genera Phyllostoma and 
Desmodus) ; but that the large and repulsive-looking vampire is 
innocent of the habit in question may briefly be made evident by 
-citing again, and a little more fully, the authority of Mr. Bates, who 
writes: ‘‘ The vampire was here by far the most abundant of the 
family of leaf-nosed bats. . . . . No wonder that imaginative 
people have inferred diabolical instincts on the part of so ugly an 
animal, The vampire, however, is the most harmless of bats, 
and its inoffensive character is well known to residents on the banks 
of the Amazons ” (‘* Naturalist on the Amazon,” p. 337).' Again, 
Mr. G. E. Dobson writes: ‘‘This species (Vampirus spectrum), 
believed by the older naturalists to be thoroughly sanguivorous 
in its habits, and named accordingly by Geoffroy, has been shown 
by the observations of modern travellers t» be mainly frugivorous, 
and is considered by the inhabitants of the c untries in which it 
is found perfectly harmless” (‘Catalogue of the Chiroptera, 
Mee Pp. 471); 
In conclusion, I cannot quite understand why my remarks 
should have led any one to believe, as one of your correspondents 
says, that I consider there is no species of bat which attacks 
human beings. I stated that the author whom I was reviewing 
Was wrong in speaking “of vampire bats as those which suck 
the blood of sleeping persons,”’ a statement which appears to me 
plainly enough to imply that there are certain other bats which 
GEORGE J. ROMANES 
Hovering (? Poising) of Birds 
LET me entreat the Duke of Argyll not to confuse the issue 
between us. I made bold to ask his Grace to draw a diagram 
showing by what balance of forces he thought a bird could be 
sustained in mid-air, motionless on motionless wings,:in a per- 
fectly horizontal wind ; and he refers me to a beautiful drawing 
of akestrel hovering, with fluttering wings, in still air. (See 
note at foot of page 161 of the “‘ Reign of Law,” 5th edition, 
1868: ‘‘ Mr, Wolf's illustration of a kestrel hovering shows 
accurately the position of the bird when the action is performed 
in still air.’”’) 
This is quite beside the mark. ‘The problem to be solved is 
not, How does a bird remain at rest in mid-air on fluttering 
wings? That question is admirably answerei in the ‘‘ Reign of 
Law” (p. 160). But the problem before us—the same that 
was discussed in NATURE in 1873-74—is simply this, How 
does a bird remain at rest in mid-air on perfectly motionless 
wings ? 
Does the Duke deny that this ever takes place? Has he | 
forgotten the letters of Prof. Guthrie and Major Herschel 
(Navurg, vol. viii. pp. 86 and 324) in which the phenomenon 
Was so graphically described? The Duke himself says 
(NATURE, vol. x. p. 262), ‘‘that under certain conditions of 
Strength of air-current a kestrel can maintain the hovering posi- 
tion with no visible muscular motion whatever ;” and compares 
the action to that of a rope-dancer ‘* standing still in some tiptoe 
attitude,” At that time he appears to have recognised the 
peculiar features of motionless hovering; but now he denies 
that he has ever ‘‘seen a kestrel’s wings motionless when hover- 
ing,” except for a moment or two, and eyen then he ‘‘ could 
detect the quivering of the quills.” 
I am really at a loss to know whether the Duke maintains 
his former position ; or whether by shifting his ground he admits 
that it is untenable ; or, lastly, whether he has not partly mis- 
apprehended the problem under discussion. 
In instancing the ‘‘hovering of a boy’s kite” the Duke 
curiously parodies the mistake which he made in his last letter, 
which required for its correction the tilting of gravity through 
a certain angle. So here, when he says, ‘‘the element of weight 
is here represented by the string, held at the surface of the 
ground,” he forgets the all-important anzle between the direction 
of gravity and the direction of the string at its point of attach- 
ment to the kite. HUBERT AIRY 
February 26 
HAVING all my life given some attention to the flight of birds, 
I may mention that I have frequently noticed both hawks and 
gulls stationary in the air, without flapping, for five or six 
seconds over the Cornish cliffs when the wind has been blowing 
off the sea, but never under the circumstances mentioned by Dr. 
Rae. I totally fail to see why Mr. Airy should be, as the Duke 
of Argyll states (NATURE, vol. xxvii. p. 387), ‘‘ mistaken in 
his description of the facts,” it having been plain throughout 
that Mr. Airy employs the term ‘‘ hovering” as equivalent to 
“‘hanging in motionless poise.” Mr. Wolf’s kestrel in the 
“Reign of Law,” p. 160, is shown as moving its wings through 
an angle of about 30°. 
Although I believe there is nothing in the etymology of the 
word ‘‘ hover”? which implies movement, yet its similarity to 
such words as ‘‘quiver,” ‘‘ shiver,” &c., may have caused the 
idea of movement to be associated with it ; but whether this be 
a “disease of language” or not, Mr, Airy seems to have most 
accurately described what is surely not an uncommon fact of 
observation. W. CLEMENT LEY 
The Auroral “ Meteoric Phenomena” of 
November 17, 1882 
Ir Dr, Groneman has established the fact that the spindle- 
shaped beam from every point of observation appeared moving 
in a straight line, that is an important point gained; but 
I fail to gather from his letter on p. 388 that there is clear evi- 
dence of this. He cites S. H. Saxby as one observer in favour 
of this, but his description appears to me very ambiguous. 
When he says, ‘‘ Its trajectory was much flatter than that of the 
stars,” what stars does he mean? If he means the stars at the 
same declination as that of the beam, viz. about 10° S., then a 
great circle undoubtedly would be flatter, but still more would a 
small -circle having its centre at the magnetic pole. On the 
other hand, H. 1). Taylor writing from near York describes the 
path of the beam as from south-east to south-west, thus making 
it a small circle curved in the wrong direction for an auroral 
arch, 
It must be remembered that it is very difficult to judge whether 
a trajectory is a straight line when it covers a great extent in 
azimuth. T. W. BACKHOUSE 
Sunderland, February 26 
IT is much to be desired that the increasing interest concerninz 
this great phenomenon should supply the only way of obviating 
the paucity and incompleteness of observations, by having a 
meeting of observers and advanced nature-students either at 
London or Bristol. The Utrecht observation says: ‘* When 
this arch had obtained the length of 90° (which lasted only a few 
seconds), a separation was made in the middle of its length,” 
&c. I think this accounts for many of the discrepancies. 
M. Groneman writes : ‘*‘ The Dutch observations confirm the 
English, only the phenomenon seems to have been of greater 
apparent size and therefore nearer.” I used to think this for 
the same reason he gives, but I now think it probable that it 
was further from the earth when it first approached, 
From Bordeaux I learn the sky was cloudy, but the aurora 
was well seen from Rome, Spezia, and Florence, and I have 
hopes of observations from the north of Italy. 
The logical position is that we must lay aside all preconceived 
| [March 1, 1883 
4 
