324 
I have already trespassed too much on the columns of NATURE, 
and I shall conclude by saying that these instances are not 
thought extraordinary here, and that the belief that cattle and 
horses can find their way “straight” is firmly held by all bush- 
men. I have heard similar instances at Lake Torrens, the Dar- 
ling River, and Maneroo. 
I am aware that they do not affect the question as to how a 
cat finds her way home when conveyed shut up in a bag, but I 
conceive that they bear out the view suggested by Mr. Darwin, 
and with which my own experience coincides. 
A. W. Howitt 
Bairusdale, Gippsland, Victoria, May 21 
Ingenuity in a Pigeon 
THE following facts (having been witnessed by myself) may, 
perhaps, be considered worthy of insertion in your journal, as 
bearing on the subject of ‘‘ Perception and Instinct in the Lower 
Animais,” which has lately been brought into such prominent 
notice. 
On the Richmond road (Surrey), at about a mile from the 
town, stands an old roadside inn, yclept ‘‘The Black Horse,” 
owned by one R. Ketley. Attached to the house are a number 
of domestic pigeons cf various breeds, chiefly “ Pouters.” 
Having occasion to wait for my pony to be harnessed at this inn 
a few years since, my attention was directed by a gentleman (a 
resident of the neighbourhood) with whom I was acquainted, to 
the strange conduct of one of these birds. 
A number of them were feeding on a few oats that had been 
accidentally let fall while fixing the nose-bag on a horse standing 
at bait. Having finished all the grain at hand, a large ‘* Pouter” 
rose, and flapping its wings furiously, flew directly at the horse’s 
eyes, causing that animal to toss his head, and in doing so, of 
course shake out more corn, I saw this several times repeated ; 
in fact, whenever the supply on hand had been exhausted. 
I Jeave it to your readers to consider the train of thought that 
must have passed through the pigeon’s brain before it adopted 
the clever method above narrated, of stealing the horse’s 
provender, 
Was not this, indeed, something more than mere instinct ? 
RIcHARD H. NaPIiER 
Upton Cottage, Bursledon, Southampton, Aug. 13 
The Origin of Nerve Force 
T notice in NATURE for July 21 a paper by A. H. Garrod, 
Suggesting that nervous force has its origin in thermo-electric 
currents due to the difference of temperature between the surface 
and interior of the body. Without presuming to any opinion 
from the physiological point of view, I venture to mention one 
or two obvious difficulties. 
Although, as the writer observes," ‘‘in cold weather the im- 
pulse to act is much more powerfully felt than in summer, when 
the air is hot, and therefore the temperature of the surface is 
higher,” yet even 98° F. (the internal temperature of a healthy 
body) is not uncommon for the air in tropical climates, where 
the natives can undergo great exertions. But, according to the 
thermo-electric hypothesis, the nerve force must in this case be 
nil, Again, temperatures of 140° to 160° F. are easily sustained 
for a considerable time in the Turkish Bath. Under these con- 
ditions the direction of the current should be reversed ; and, even 
supposing that positive and negative currents both acted in the 
same sense on the muscles and nervous ganglia, it would seem 
that there must be an instant of transition when the two should 
be balanced, and nervous force at zero, and the powers both of 
sensation and motion lost with it. 
The thermo electric theory is not required to explain the cases 
to which Mr. Garrod alludes. We have only to consider that 
the body must be kept at a constant temperature of about 98° F., 
while heat is being continually evolved internally by nervous and 
muscular action, to see that the surface of the body must be 
cooler than the interior in order to get rid of the superfluous heat 
without consumption of work in increased perspiration and eva- 
poration. At high external temperatures there will naturally be 
disinclination to muscular exertion ; not only because it pro- 
duces heat which tends to upset the equilibrium of temperature, 
but because the force that would have been expended in it is 
consumed in increased action to get rid of the heat. That the 
exhausting effect of hot water is much greater than that of hot 
air is accounted for both by its greater conductivity and specific 
NATURE 
——$—<—— $$” OS anor 
[ Aug. 21, 1873 
heat, and still more because it checks evaporation, which is one 
of the most powerful outlets for waste heat. It must be familiar 
to everyone that rapid exhaustion is produced by immersion not 
only in hot water but in that of almost any temperature. Taking 
7o° as an average external temperature, we shall find that im- 
mersion in water at 30° would be quite as rapidly destructive of 
nervous energy as in that of 110°; and that while air of the latter 
temperature could be sustained by theynaked body for long 
without inconvenience, that of 30° would be rapidly tatal unless 
the temperature was kept up by violent exercise. 
Supposing the brain to be really colder than the blood, I shall 
be glad if some physiologist will inform me if this is not due to 
the consumption of heat in building up the complicated and un- 
stable matter of the brain from the comparatively stable and 
simple constituents of the blood, and in this case, if there is any 
difference of brain temperature between times of rest and nuiri- 
tion (sleep) and those of active exertion. 
Knowing as we do that chemical action is constantly going on 
in the body and that electrical disturbance is an almost constant 
result of such action, it seems hardly neces:ary to look further 
for the source of nerve force, though we are in almost complete 
ignorance of the details of its production. 
Henry R. PRrocTer 
The Flight of Birds 
Your correspondent, J. Guthrie (vol. viii. p. 86), has struck 4 
note which will, I think, echo. The question he raises is one which 
has exercised more minds than one. It has been present to me 
individually almost ever since I was able to reason. The oppor 
tunities enjoyed by exiles, especially in tropical coun'ries, for 
the study ot the phenomenon of a body, poised in mid-air, with 
no apparent support, is considerable, owing to the boldness and 
number of kites and birds of that class. I have watched them 
from the point of view—figuratively speaking—of your Cape 
correspondent, scores of times, and sometimes under peculiar 
conditions: but I am unable to add anything certain to the bare 
statement that birds of prey ca# maintain a position of absolute 
apparent rest. . i 
it is some fourteen or fifteen years since I first watched an 
eaglein a telescope, with a view to test an explanation—the same 
as that suggested by Mr, Guthrie—hazarded as a conceivable 
po:sibility by my father, long before. Since that day I have 
had innumerable opportunities for close watch—some of which I 
will describe—and never have I seen anything to support it. 
Not to go back too far, as I must trust to memory, [ was, 
two or three years ago, on the summit of a long-backed solitary 
hill, 500 or 
Southern India. There was alight breeze blowing, and I saw an 
eagle stemming it, on the leeward side of the hill, which was steep. 
Sometimes he was within (say) fifty yards, and having a goo 
glass at hand, I rested it ona stone heap, and watched him. It was 
irequently possible to see him thus, stationary in a motionless ficld’ 
of view, at anapparent distance of 10 or 12!t. Not a feather 
quivered : the head was turned from side to side as he scrutinised 
the hill-side : occasionally a foot was brought up to the beak; 
the roll of the eye was perceptible: but otherwise he was af 
vest to all appearance, Of course the tips of the wings came in’ 
for a share of my scrutiny. They may have been quivering, but 
they looked as steaciy as those of a stuffed specrmen. And here’ 
I may observe, that for this appearance to be compatible with’ 
an unperceived vibration, the position of rest must have existed’ 
alternately with successive excursions, and the time occupied by’ 
the latter must have been insignificant as compared with the’ 
duration of rest. I find it impossible to accept this explanation, 
even as a first step, and need not inquire how it would produce’ 
the supporting effects. The tail, 1 should mention, was not at 
rest. It was frequently feeling, as it were, the passing breeze. _ 
It is tobe understood that in the course of frequent changes of 
general position, I had the bird under examination from different 
directions—not always of course so favourably, 
On another occasion I spent a fortnight on the summit of a- 
peculiar hill in this neighbourhood, with nothing to do but 
recruit as fast as possible. The hill resembles a dish-cover at- 
top, and being the resort of fugitives from the dust and drought 
and heat of Bangalore in April and May, who occupy every avail« 
able dwelling on a very restricted space, there is plenty to attract’ 
the kites from far and wide, to say nothing of vultures. There 
are two or three kinds of kite, but for the present subject they 
are all the same—fine, powerful, bold birds, with a stretch of 
600 ft. high, in the Coimbatore plains of 
