October to spring _into water_, but they give us no direct proof that
they constantly remain submersed. The presence of the observer may
alarm the frogs, and thus prevent [p148] their putting their heads
above the water, so that the assertion is but a negative kind of
proof that they remain so long under the water without coming up to
respire, as some affirm. M. Bose declares he watched frogs approach
the surface at regular periods every day during the winter season.
Under the most favourable circumstances Dr. Edwards found that frogs
could not remain submersed, in winter, more than two days and a half.
Frogs are less active during winter than at the other seasons, but
they never lose their motion. Were it true, as Spallanzani thinks
it is, that they remained so long under water, it is probable that
they would become frozen in winter and die. Spallanzani derives
his opinion from what occurs with fish, forgetting that frogs are
amphibious, and live as well on land as in water; whereas fish are
limited to a watery medium, and can, therefore, furnish no example.
Dr. Edwards found that frogs, placed in certain quantities of aërated
and non-aërated water of an equal temperature, lived longest in the
_former_; but that the difference was not constant in its results,
being often twice as long in one case as in the other, as to the
duration of life.
The next inquiry regarded _stagnant water renewed at intervals_, and
in this the duration of life was prolonged beyond the term of the
last experiments, and even to eight days. During winter when the
temperature was lowest the frogs remained active, though less so than
in spring.
The conclusions to be drawn from these experiments are, that frogs
pass the winter _in an animated state in water_, not becoming
stiffened as in ice, and that they need not to approach the surface
of the water in order to respire, provided the water they inhabit
be _renewed at intervals_; but if the water be not renewed, or if
disaërated water be employed, the frogs perish.
Considering that these animals are truly amphibious, these results
are very curious; and it is interesting in a physiological point of
view, to know that frogs are able to respire the air contained in the
dense medium of water for an indefinite period, and just as easily as
they breathe the finer medium on land.
Respecting the action of aërated water on the skin, the conclusion
drawn seems to be correct, that it must be from _cutaneous_
absorption that the air contained in the water promoted the
continuance of life in Dr. Edward’s experiments upon this point,
since the animals were in a state of _asphyxy_ regarding respiration
by the lungs; and that no [p149] air entered in combination with
water was shewn from Dr. Edwards _never having seen water in the
lungs_. Therefore, unless the air acted on the blood through some
other organ, the lives of these animals would be definite and
shortened, even though the water be renewed from time to time, and
their _asphyxy_ would be complete and continued. And since the skin
is the only organ in contact with the air, it is fair to conclude
that it is the medium of aërial absorption.
When the _webs_ were examined under water, these membranes indicated
the action of air upon their blood-vessels, by the bright tint of the
blood.
Spallanzani imagined that frogs perish sooner in _running_ than
in _stagnant_ water; but Dr. Edwards having secured some of these
animals in ten feet of the Seine, whilst others were simultaneously
placed in _unrenewed stagnant water_, he found the latter did not
survive many hours, and the former lived a long time.
In order to fix the limits of this kind of existence, frogs were
placed in _renewed aërated water_, and with a temperature never
forced beyond ten degrees they were found to live _in all seasons
of the year_; but when the temperature was elevated from twelve to
fourteen, they died in a few hours. In running streams they lived
longest, and at twelve degrees they were thus more favourably placed
than in stagnant water, _at a lower temperature even_, and taking
the precaution to renew the water daily; and at seventeen degrees
in running water they died prematurely. Toads exhibited the same
comparative results, but they lived the longest.
It appears, therefore, that water contained in vessels is less
favourable to the lives of these animals than running streams,
although the water and the temperature were identical. Probably the
great advantage of running water is its _constant and unceasing
renewal_. The separate and comparative influence of air, water,
and temperature, being thus investigated, the combined action
of the three physical agents was next inquired into, and it is
demonstrated that frogs submersed in water are influenced by three
circumstances,—1. the presence of _air_ in water; 2. the quantity of
its renewal; 3. the _temperature_ of the medium. If the manners of
frogs be closely examined, they appear to live in water under very
considerable influence from the atmosphere.
From circumstances developed in the foregoing experiments, _cutaneous
respiration_ seems to be pretty evidently indicated. A chapter is,
therefore, devoted to this subject, one that is not well known,
although pulmonary respiration is [p150] generally understood. In
frogs, the function of pulmonary respiration is united with that
of deglutition, and the air enters only by the nostrils, the mouth
being closed during respiration. While the mouth remains open, the
action of deglutition is stopped, and, therefore, the animal does
not then breathe. Dr. Edwards availed himself of this circumstance
by gagging the mouth so as to keep it open, and thus prevent the
air from entering the lungs. The frogs were sufficiently exposed to
moisture and renewal of air to their bodies: the results were, that,
at twenty-four degrees, five frogs so placed died next day, and one
lived a week.
Dr. Edwards immersed some frogs in wet sand, and adopted an improved
method of excluding air from the lungs, and some of them lived
twenty days. Hence it evidently appears that air influences the
skin materially, and counterbalances the asphyxious state induced
by obstructing the air’s passage to the lungs. By adopting other
methods, the existence of frogs was prolonged to thirty or forty
days. It is, therefore, sufficiently proved that the blood undergoes
its necessary changes from atmospheric influence through the medium
of the skin, although in a minor degree compared with those which it
passes through from pulmonary respiration. Frogs are thus shewn to
possess a double source of respiration.
By substituting _oil_ for water, frogs immersed in this fluid died
in a few hours, being at liberty to breath the air on its surface.
And, when plunged into oil, with the means of breathing by the lungs
arrested, they lived an equal time with frogs simultaneously placed
in water without power to respire. A comparison was instituted with
frogs in oil and in water, being allowed to breathe air, when the
difference was found to be very considerable in favour of the aquatic
bath. These circumstances shew, that, even with the feeble succour of
the air through the skin, absorbed from the water, the respiratory
function was far more prolonged, than in the case of the obstruction
afforded by the oil. Thus we have abundant evidence of the double
function by which frogs are maintained, from the action of the air on
the skin and the lungs; and this appears to be the means of existence
among _amphibious animals generally_.
It may be asked why these animals die in deep water when prevented
from approaching the surface? It appears that, having expelled the
respired air from their lungs, which is imperfectly renewed from the
water, they become specifically heavier than the water, and unable to
rise from the bottom; and thus placed, the duration of their lives
depends upon [p151] the resistance offered by their constitutions
to the depressing effects of a state of asphyxy while remaining
submersed.
Dr. Edwards next proceeds to inquire into the effects of
TRANSPIRATION. A liquid transfusion from the skin of animals is
constantly going on, either in the form of vapour or of fluid in a
denser state.
The latter constitutes sweat. This phenomenon exhibits great
variations, and it is important to know what diminution of weight the
body suffers in different circumstances. In the course of an hour
remarkable fluctuations occur.
Dr. Edwards suspended frogs, toads, and salamanders, in a _calm air_,
weighed them, and noted the results, which, though very changeable
in an hour, were generally uniform in three, and in nine hours they
averaged an equal result. The successive diminution in the mass of
fluids was evident.
The results were modified by the alternate position of the animals in
a body of air in repose, or agitated by a draft. And these results do
not appear to depend upon any principle of vitality, for they take
place equally in death and in life, and indeed among unorganized
bodies, as, for example, lumps of charcoal soaked in water. Therefore
the cause of the phenomenon of transpiration seems to be referrible
entirely to physical agents. The _motion of the air_ seems to be its
exciting cause; for even when, to all appearance, it is calm, it is
in reality agitated more or less, and produces a sensible evaporation
from the skin. But the difference between the effect of calm and
agitated air is remarkable; for in a draft, the animals exposed to
it sweated away double the quantity of liquid compared with those
confined in a room shut up. The amount lost was proportioned to the
_intensity of the wind_, and reached a triple amount over those
animals in stagnant air; and this fact explains the variations
noticed from hour to hour among animals exposed to currents of air.
The transpiration which occurs in very moist air, always amounts to a
diminution of weight; but in dry air it is five or ten times greater;
and when the influence of a moist state of the atmosphere is compared
with that of a dry state, the amount of evaporation is equal to that
of a dry and calm air.
Transpiration may, therefore, be referred to _the agitation of the
atmosphere_ for its exciting cause, beyond any modifications of its
_density_. And, although an elevated temperature be favourable to
transpiration, its modifying influence is less than that of other
causes.
In comparing the effects of _absorption_ and _transpiration_, [p152]
in water and in air, frogs were found to gain an addition to their
weight according to the term of their continuance in the former
medium. An absorption of water was rendered evident by the loss of
bulk it had sustained, when measured after the experiment.
Thus, when the comparative influence of water and air is estimated,
the former appears to be absorbed, and adds to the weight of the
body; and the latter tends to diminish the weight, by different and
fluctuating degrees of evaporation taking place, and dependent much
more on the degree of motion in the air, than on its dryness or
humidity: these last conditions modify evaporation in a minor degree,
when compared with the influence of a current of air.
The celerity of _absorption_ exceeds that of _transpiration_ six
times, in the most rapid cases. It therefore results, that the losses
by _transpiration_ in air should be repaid by absorption of water
in a much less time than the expenditure occurs. But the decrease
of weight is not prolonged; it is sudden, and not continuous,
alternating with augmentation of weight, by absorption of liquid
going on in a ratio superior to the loss; and thus nature’s provision
is manifested for the nutriment of the body.
With this last inquiry Dr. Edwards concludes the first part of
his work; and it is observed, that, with regard to transpiration,
the losses of weight have been considered without reference to
the existence of any other influence than water. The losses by
transpiration have been examined generally without regard to the
matters lost. What relates to water differs essentially in one
respect from that which regards the air. The losses sustained by the
body ought to be more particularly examined. Temperature and loss of
time require estimation. An excretion of _solid_ matter evidently
takes place; for the water, in which animals are submersed, becomes
turbid, especially in hot weather, and it sensibly contains animal
matters, affecting the weight of the body in water.
When animals are submersed in water, their skins exercise two
functions, acting inversely in determining their weight. And it
results, from comparative experiments, that the _absorption at
zero_ exceeds the _loss in water_; while at thirty degrees the
_loss_ exceeds the increase by weight from absorption; and the
higher the temperature, the greater is the excess in the discharge
of animal matters. We may therefore presume, that the agency of
_temperature_ produces analogous effects, upon aërial transpiration,
to those before observed [p153] in other inquiries; and the effects
of _dryness_ and _moisture_ in the air produce a minor degree of
influence also, when compared with _temperature_, on the losses of
animal substances.
We have been thus minute in our analysis, because the subject of
it is new to science in its present shape, and of a high degree of
interest. Dr. Edwards’s researches among the different classes of
animals have tended more to the illustration of the influence of
physical agents upon life than any previous authorities; and the
persevering industry, accuracy of observation, and patient inquiry
which he has evinced in his investigations among cold-blooded
animals, have placed this department of the creation in a point of
view at once curious, interesting, and valuable to science. We attach
the greater importance to this part of the author’s work, as it is
a ground on which he may be consulted, and quoted as indisputable
authority, until equal inquiries have shewn him to be fallacious.
Our limits will not at present permit us to proceed farther in our
analysis, and we must refer the remainder of the book to a future
opportunity. The subjects of the three other parts, though greatly
extended, will not probably require such minute analysis as those
novel experiments which form the subject of the first part; but we
imagine that the application of the principles laid down, in the
previous inquiries, to human physiology, will be found not less
interesting than those which relate to the natural history of the
lower orders of the animal creation.
_An Account of Professor Carlini’s Pendulum Experiments on Mont
Cenis_.
We believe that no account of Professor Carlini’s pendulum
experiments on Mont Cenis has hitherto appeared in the periodical
scientific publications of this country: the experiments are,
however, well deserving of such notice, having been conducted with
great care, and having had a specific object in view, which object
seems to have been satisfactorily accomplished. The following
brief account of them, taken from the original memoir published in
the Appendix to the “Ephéméride di Milano” for 1824, may not be
unacceptable to those of our readers who interest themselves in
subjects of this class.
The length of the simple pendulum vibrating seconds is a [p154]
measure of the intensity of gravitation; _i. e._ of the excess of the
force of gravity over the centrifugal force. In consequence of the
ellipticity of the earth, and of the difference in the direction of
the two forces, the intensity of gravitation varies according to the
different latitudes. It also varies, in the same latitude, according
to the greater or less elevation of the pendulum above the level of
the sea; _i. e._ according to its greater or less distance from the
centre of the attracting force.
Had the earth a perfectly level surface, such, for instance, as
it would have if it were everywhere covered by a fluid, the force
of gravity, in receding from the surface, would diminish in the
duplicate proportion of the distance from the earth’s centre. In the
actual state of the globe, however, its continents and its islands
are raised above the general level of the sea by which it is only
partially covered; and if a pendulum be raised, on the surface of
the land, to a known elevation above the sea, the diminution of
gravity will not be, as in the more simple case, proportioned to the
squares of the respective distances from the earth’s centre, but that
proportion will require to be modified, by taking into account the
attraction of the elevated materials, interposed between the general
surface and the place of observation.
When pendulums are employed in different latitudes, to obtain the
ratio of gravitation between the equator and the pole, for the
purpose of deducing the ellipticity of the earth, all the places
of observation, being on land, are more or less elevated above the
sea; inland stations, in particular, are sometimes at considerable
elevations: to render these results comparable one with another,
it is necessary to reduce each result to what it would have been,
had it been made at some level common to all the experiments; and
the surface of the sea has hitherto been taken as that common
level. Previous to the publication of a paper of Dr. Young’s in the
Philosophical Transactions for 1819, the consideration which we have
mentioned, that of the attraction of the matter interposed between
the place of observation and the level of the sea, was generally
unheeded in estimating the allowance to be made for the reduction
of different heights to the common level: in that paper, however,
Dr. Young took occasion to point out the probable effect of [p155]
the interposed matter in modifying considerably the usual allowance;
that, supposing its density to be about half the mean density of
the earth, the effect of an hemispherical hill of such matter, on
the summit of which the pendulum should be placed, would be to
diminish the correction, deduced from the duplicate proportion from
the earth’s centre, about 1/5th; that, in like manner, a tract of
table-land, considered as an extensive flat surface, of the same
relative density, would diminish the correction about 3/8ths; and
that, accordingly, in almost any country that could be chosen for
the experiment, the proper correction for the height would vary,
according to the form and density of the interposed materials, from
rather more than a half to rather less than three-quarters of the
usual allowance. This view has been subsequently acted upon by the
English pendulum experimentors, in reducing their observations;
but it has not been yet adopted by the French. The experiments of
Professor Carlini were calculated to afford a practical illustration
of the correctness of Dr. Young’s reasoning.
Professor Carlini was engaged, in the summer of 1821, in concert
with Professor Plana, in determining the amplitude of the celestial
arc between the Hospice on Mont Cenis and the Observatory at Milan,
by means of fire-signals made on the Roche Melon, and observed
simultaneously at Milan and at a temporary observatory established
at the Hospice. Whilst thus engaged, Professor Carlini, being
stationary for several days on Mont Cenis, and obliged to have time
very accurately determined, for the purpose of comparing with the
observatory at Milan, availed himself of the opportunity to employ
a pendulum apparatus of the same general nature as that used by M.
Biot at Paris, which had been prepared at Milan some years before,
under the direction of a commission of weights and measures, with the
view of determining the value of the divisions of the national linear
scale. As this apparatus differed in some few particulars from the
original employed in France, we shall briefly notice the differences,
presuming our readers to be acquainted with the apparatus of MM.
Borda and Biot.
1. In the Milan apparatus, by means of two microscopes furnished with
wire micrometers, the length of the pendulum [p156] may be measured
without touching it; without approaching it; without even opening the
case which contains it. The measure is obtained by bringing the wires
in contact with the images of the knife-edge suspension, and of the
upper and lower borders alternately of the platinum disk suspended to
the thread: thus preventing the risk of deranging the equilibrium,
and avoiding the effect which the heat of the body might have on the
dilatable metallic thread.
2. The half sum of the distances taken between the suspension, and
the upper and lower edges of the disk, gives the distance of the
centre of the disk itself; without measuring its diameter with a
compass, an operation exceedingly difficult to execute with the
necessary precision. By this apparatus of microscopes the length may
be measured at pleasure, even during the time of oscillation; and
being attached to the wall, instead of supported by the floor, the
risk of derangement by the tread of the observer is avoided.
3. The pendulum, and the clock by which its oscillations are
measured, were not, as usually, near together and resting on the
same base, but were perfectly separated. The coincidences of the
oscillations were observed, by bringing the image of the pendulum of
the clock, reflected by means of an oblique mirror, in contact with
the image of the simple pendulum seen direct through a telescope. By
this modification the risk of the mutual influence of the pendulum
and the clock is avoided.
4. The disk was attached to the thread by means of knots in the
thread itself; avoiding the correction for the small cup usually
employed for that purpose.
5. An alteration was made in the weight and shape of the knife-edge
suspension; reducing its weight to about 10 grains, and giving it the
shape of a rotella, instead of that of a triangular prism.
The simple pendulum and microscopes were attached to a strong
wall, in a room on the ground floor, contiguous to the temporary
observatory, and well sheltered from the sun and weather. The clock
with which the pendulum was compared, was supported by a pyramid of
masonry resting on the ground, and occupying the middle of the room.
The experimental length between the microscopes was referred to three
standard metres, [p157] in perfect agreement with each other: one
received from Paris by the Commission of Weights and Measures at
Milan; a second brought more recently from Paris by Conte Moscati;
and a third in the possession of the Royal Academy of Turin.
The experiments were commenced on the 3rd of September, and
terminated on the 27th, being interrupted by M. Carlini’s absence
at Chambery from the 7th to the 12th. The distance between the
microscopes, and the oscillations and length of the pendulum,
were measured alternately. Thirteen independent results were thus
obtained, of which the greatest discordance from the mean was not
more than 13/10000ths of a British inch. The mean result was 39.0992
British inches, the length of the pendulum vibrating seconds in a
vacuum, at the place of observation on Mont Cenis, 1943 metres, or
6374 feet above the sea, in the latitude of 45° 14′ 10″. To compare
with this determination, we may obtain a tolerably fair approximation
to the pendulum at the level of the sea in the latitude of 45° 14′
10″, such as its length might have been found, if the mountain could
have been removed and the pendulum placed on its site, by deduction
from the lengths actually measured with a similar apparatus, on the
arc between Formentera and Dunkirk, at stations not far removed from
the level of the sea, in the adjacent parallels to Mont Cenis, and in
the countries adjoining. Of these there are five, not including the
station at Clermont, in consequence of its great elevation: they are
as follows:—
° ′ ″
Dunkirk 51 02 10; its pendulum at the level of the sea = 39.13771
Paris 48 50 14; " " " " 39.12894
Bordeau 44 50 26; " " " " 39.11295
Figeac 44 36 45; " " " " 39.11212
Formentera 38 39 56; " " " " 39.09176