NATURE 
249 
3 were found in great abundance in association with these sponges. 
They were generally of an elongated pyriform shape (the ‘‘ace- 
rate” form of Bowerbank). He supposed they were originally 
calcareous, but had become siliceous during the progress of fossili- 
sation. —The next communication was from Dr. Carpenter upon 
“* Different modes of Computing Sanitary Statistics, with special 
reference to the opinions of Mr. Andrew A. Watt.” Upon this 
- subject, which related exclusively to the statistics of population 
of the city of Montreal, there was an animated discussion. 
Norwicu 
Naturalists’ Society, November 30.—The Rev. J. Cromp- 
ton, the president, in the chair. Mr. Southwell read a long and 
interesting paper ‘‘On the Flight of Birds.” The seeming im- 
possibility of a heavy body supporting itself in mid-air, gliding 
along, changing its direction at will, apparently violating all the 
~ known forces of nature, is sufficiently astonishing to attract the 
attention and engage the researches of scientific men; and yet, 
till of late, the subject has been neglected, or the theories formed 
to account for so remarkable a phenomenon have been altogether 
erroneous. ‘The great stumbling-block to the arrival at the 
‘truth seems to have beer the very natural idea that buoyancy was 
_ the first essential to flight, whereas it is now shown, that so far 
" from being an essential, it is an actual impediment. Hunter dis- 
covered the presence of air-cells in the bones and dispersed over 
various parts of the bird’s body, and it was believed that by this 
~ means heated air was used to render them lighter, and that it was 
- possible by thus inflating the body to increase the bulk, at the 
same time decreasing the weight ; forgetting that additional 
bulk without a corresponding increase of weight would but 
enlarge the surface presented to atmospheric resistance, thereby 
rendering the too buoyant body of the bird the sport of every 
wind that blows. Sir Charles Bell follows up this idea of exces- 
sive lightness ; but Captain Hutton, in a paper on ‘‘ The Birds 
inhabiting the Southern Ocean,” shows that in order to bring 
the specific gravity of the albatross to that of the atmosphere, 
the air-cells in its body should contain 1,$20 cubic feet of air 
_heated to 108 degs.—equal to a sphere of more than 15 feet 
in diameter; or, in other words, they must be 1,200 times the 
size of the body itself, ‘‘ which,” he adds, *‘ would give it, when 
flying, an aldermanic appearance which I have never observed.” 
It is obvious, therefore, that the air-cells are not intended to aid 
the bird in flight by rendering it lighter than the air itself. 
~ After referring to the opinions of Sir Charles Bell, Mr. Southwell 
gave an account of the principles enunciated in France by M. de 
~ Lucy, who has shown that three great properties are absolutely 
essential in all winged animals—(1) weight, or the force of 
_ gravity ; (2) surface, or the area presented to atmospheric resist- 
“ance ; and (3) force, or the power of projection. Without weight 
the object might float, but it could never fly, there would be no 
resisting force to form a fulcrum to its movements, and it would, 
~in fact, be part of the atmosphere and subject to it, wafted hither 
and thither without the power of resisting. The bird being 
elevated in the air, possesses, in virtue of its weight, a force 
always exerting itself in a downward direction, thereby producing 
motion, which, if it has the power to control, will prove the main- 
spring of its flight. In order to counteract this downward 
motion, surface is called into request. The expanded wing is 
presented to a column of air perpendicular to itself, and a new 
Jaw of nature comes into operation—that of atmospheric resist- 
ance. This is not sufficient to counteract the force of gravity 
without some mechanical action on the part of the bird, but it 
would in a great measure break the force of the fall, causing it 
to descend in a series of zigzags, as a sheet of paper falls from 
-a balloon. We should expect to find the surface increase in pro- 
portion to the weight of the animal; but, strange to say, it has 
been shown by M. de Lucy that the extent of surface is always 
in an inverse ratio to the weight of the winged animal. The 
heavier the animal, the smaller its wing surface, referred to a 
fixed standard. This is shown remarkably in flying insects ; the 
body is very light, but the wing surface is enormous. ‘The bird 
would soon be brought down from mid-air but for the muscular 
power of depressing the expanded wing forcibly and rapidly so as to 
cause the elastic column of the air beneath to rebound with sufficient 
force to destroy the remaining effects of gravity and so to equalize 
all the forces as to leave the bird reacly to pursue its course at will. 
The most striking thing about the skeleton of a bird is its great 
lightness combined with strength, By a beautiful arrangement, 
the greatest power is given tothe wings. ‘The front part of the 
wing, that first presented to the air in forward flight, is stiff 
and unyielding, well adapted for cutting its way through the 
air; the other feathers become weaker and more pliable as they 
are placed nearer to the body of the bird. The feathers, which 
are divided into two portions by a nearly central shaft, overlap 
each other, the anterior web, which is the strongest and stiffest, 
being uppermost. When the down stroke is delivered, the 
wing presents to the air an impenetrable and unyielding surface, 
but when the corresponding up stroke is made, the yielding 
posterior web of each feather becomes depressed by the resist- 
ance of the air above, thus separating the feathers so as to 
allow of the free passage of the air; by this means giving the 
maximum amount of force to the down stroke, which would 
otherwise be neutralised by the resistance of the up stroke. But 
this is not all; the under surface of the wing is more or less 
concave, while the upper surface is convex. It is obvious, 
therefore, that when the up stroke is made, the air will rush 
off and through the wing in all directions, but when the motion 
of the wing is reversed, the air will be gathered up in its 
hollow, and the resistance immensely increased. By a wonder- 
ful contrivance, the same stroke which elevates the bird gives 
ita forward motionalso, Mr. Southwell then gave an elaborate 
description of the mode in which forward motion is effected, 
from the Duke of Argyll’s work, ‘‘ The Reign of Law.” Those 
birds with very long and pointed wings possess the greatest 
powers of flight; as, for instance, the sharp-winged martin 
for speed, and the long-winged albatross for both speed 
and endurance. The power of tuming in flight appears to 
be the result of an involuntary effort, as we turn or incline to the 
left or right in walking. It is a matter of considerable difficulty 
to obtain reliable data as to the actual velocity with which birds 
travel through the air. The flight of a hawk, when its powers 
are fully exerted, has been calculated at 150 miles an hour ; the 
usual flight of the eider duck at the rate of 90 miles an hour. 
Audubon estimates the flight of the American passenger pigeon 
at a mile a minute, and the carrier pigeon to possess, probably, an 
average of 50 or 60 miles in a long flight, although over short 
distances, as when pursued by a hawk, its speed is much greater. 
The flight of rooks ‘‘going home to bed with full stomachs,” and 
taking it easy, Major Holland estimates at about 26 to 30 miles 
an hour ; the speed of the albatross whilst coursing in company 
with a ship, he reckons at about 90 milesan hour. The flight of 
other birds, such as the swallow, the eagle, and the peregrine 
falcon, has been estimated as of much greater speed. The 
power of passing with ease and rapidity over long distances is of 
vast importance to birds living in communities. Rooks, for 
instance, would soon exhaust the supply of food in their own 
neighbourhood, Mr. Stevenson is satisfied that the guillemots 
and gulls seen feeding in Yarmouth and Lowestoft Roads in 
summer, come from the great nesting-places on the Yorkshire 
coast ; and Mr. Yarrel states, on the authority of Dr. Jenner and 
the Rev. N. Thornbury, that the domestic pigeons about the 
Hague ‘“‘ make daily marauding excursions at certain seasons of 
the year to the opposite shore of Norfolk, to feed on yetches—a 
distance of forty leagues.”” Mr. Southwell quoted many instances 
of the extraordinary power of birds to endure protracted flights ; 
and concluded by saying that man with all his boasted skill has 
not been able to construct a machine to enable him to navigate 
the air, and, even with the bird before his eyes, he has failed to 
learn its lesson. In the discussion which ensued, Mr. Southwell 
said he hoped his paper would attract attention to the subject of the 
flight of birds, as very little was known about it; and the very 
fact that in modern days men attributed the powers of flight in 
birds to the air-cells being filled with hot air, showed how little the 
principles of flight must have been considered. 
Paris 
Academy of Sciences, December 20.—M. E. Becquerel 
presented a note by M. J. M. Gaugain on the electromotive forces 
developed by platinum in contact with various liquids, The 
author stated that when two platinum electrodes, ot j/atinzsed, 
have remained in an acidulated liquid until they furnish no 
sensible current, if one of them be washed in distilled water 
and dried with blotting paper, it becomes negative on being again 
placed in the liquid. The opposite effect is produced with 
solution of potash. The effect in the latter case is much greater 
when the electrodes are platinised. The author ascribed this 
phenomenon to a modification of the electrodes consisting 
in a superficial adherence set up between the platinum and 
the acid or alkaline substance. He also remarked upon the 
difference of function in platinised and non-platinised electrodes, 
