Chapter IX: Letter XIX: gives a definition of the ellipsis, which would be a (3)

Dr. Edwards next proceeds to investigate the phenomena of _asphyxy_ produced by _strangulation_, or the mechanical obstruction to the access of air to the lungs, and consequently to the blood. The same animals were employed. When the windpipe was rendered impervious by ligature, the muscles of the animals seemed to be paralysed directly; and although their motions became subsequently revived at times, [p144] they never altogether recovered their perfect freedom. As a comparative illustration, an equal number of frogs were submersed in water, all of which died in about ten or eleven hours, while those which were strangled lived from one to five days. Salamanders continued active longest, and one did not cease to exist till the eleventh day, although during this time he was in a complete state of _asphyxy_ from perfect strangulation.

Dumeril once found that a salamander lived a long time after decapitation, even when the cicatrix of the wound was healed so as to stop all access of air to the lungs.

In comparing the effects of strangulation with those of submersion or drowning, it is to be supposed either that these animals exist a limited period without the necessity of the nervous system being in contact with atmospheric air, or that the air influences their blood through the integuments of the body. Accordingly Dr. Edwards put this to the test by making experiments upon _cutaneous respiration_.

Spallanzani found that the exposure of cold-blooded animals to the air was attended with exudation of _carbon_, a phenomenon similar to that of respiration. There appears, however, to be some source of error in these experiments, for Spallanzani removed the lungs, and this operation rendered the animal liable to the absorption of air and loss of blood. Dr. Edwards sought to effect the same purpose by a different and more successful measure. He also confined frogs in vessels of atmospheric air, and fastened bladders round the head and neck, tight enough to stop the entrance of air to the lungs. At the expiration of two hours the air was examined in the bladder, and it was found to contain an excess of _carbonic acid_. The same result was obtained from salamanders. It appears, therefore, that while air is in contact with the skin, _carbon_ is given out; but whether this be the effect of exhalation merely, or that _oxygen_ is actually absorbed, and _carbon_ transpired, is a question which led to further inquiries. Dr. Edwards, therefore, inclosed cold-blooded animals in _solid substances_, in order to determine the influence of dark-coloured blood, free of all external agency, in the production of chemical changes, and to observe its sensible effect upon the nervous system.

In the year 1779 three toads were confined in a box hermetically sealed, and so deposited in the Academy of Sciences. Eighteen months after, the box was opened, and one toad was found dead. These animals have been found alive in blocks of coal after an imprisonment of some years, and have [p145] also been sealed up during similar periods without perishing. Possibly some hole or crevice might have admitted a little air. But, in Hevissant’s experiment of 79, care seems to have been taken to obviate this suspicion.

Dr. Edwards, however, determined to put the question to the test. He enclosed ten out of fifteen frogs in thick wooden boxes, and filled the interstices with plaster, covering them over with the same substance, the toads lying each in a central hole or bed. The other five toads were at the same time submersed in water, and at the expiration of eight hours they were found to be dead. In sixteen hours more, one toad was taken from a box and found to be lively, and was reconsigned to its prison. On the sixteenth day the toads in the boxes were discovered alive, and thus the fact was established that these animals can live far longer in a state of asphyxy confined in solid substances, than when submersed in water. This was confirmed by repeated trials on salamanders, frogs, and toads. The frogs perished quickest.

Thus an extraordinary fact is established, as regarding reptiles, since it affords an exception to the general rule that _all animals require a_ CONSTANT _supply of fresh air for the maintenance of their existence_.

Similar trials were repeated in sand, and with the same results.

Dr. Edwards found that although a certain quantity of air enters the boxes and sand, yet that it is far too little to maintain life. His conclusion, therefore, stands, that animals of the kind employed can live longer in _solid substances_ than in a limited quantity of _dry air_.

It remains, however, to be considered in what manner these animals have their lives extended beyond those exposed to the action of a body of air. Dr. Edwards supposes the _moisture_ of the sand to be one cause, since in the dry air the animals become _desiccated_, the cutaneous transpiration being lost in one case, and retained in the other, by the exclusion of air. A rapid and abundant transpiration from the body, united with deficiency of air, seems to be a greater cause of dissolution than confinement in solid substances wherein there is no waste by transpiration.

The author’s inquiries are next directed to the influence of _temperature_ upon animals of cold blood, and two and forty experiments are practised upon this subject, from the month of July to September following, during which period frogs were submersed in aërated water, with a view of settling the duration of life, acted on by varieties of temperature. The [p146] continuance of life, generally, in these experiments, varied from one to two hours and twenty-seven minutes. The mean term of life was one hour and thirty-seven minutes, as averaged in July, and in September one hour and forty-five minutes, the two extremes of the seasons approximating the effects. The duration of the frog’s existence was greatest in the greatest depression of temperature. Thus at ten degrees the duration of life was more than double what occurred at sixteen or seventeen degrees, and at zero it was about triple. As the heat was increased, the duration of life was diminished; at forty-two the frogs died, and in the lowest temperature they lived longest.

It appeared that at zero the frogs did not become stiffened, but retained their motion, and their resistance to the frozen state is the cause of the continuance of their existence at a low temperature. The cause of this resistance is to be found in their peculiarity of constitution. Toads produced similar results.

It may be alleged that frogs naturally live in climates at from forty to forty-two; but, it is to be observed, that they are then placed in a situation of liberty to come to the surface of the water to respire when they please; whereas in these experiments their respiration is limited, from their inability to reach the surface.

Taking a wider range of temperature, Dr. Edwards sought to ascertain the influence of the _seasons_. In July and September frogs were found to live from one to two hours and twenty-seven minutes in aërated water at fifteen and seventeen degrees. In November they died at the end of more than double this period, under the same temperature, and all other circumstances being similar excepting the season. As the autumn advanced life was prolonged.

To what are we to ascribe the modifications of the seasons? Probably to circumstances appertaining to the intensity of light, to electricity, to temperature, to the pressure of the atmosphere, to dryness and moisture, &c.? Such existing causes naturally suggest themselves. But it appears that little or no account can be rendered as to pressure, since its variations were too trifling during the two seasons. Moisture could not effect an influence, because the experiments were performed in water. The motion of the air was also obviated. Of all the suggested modifications _temperature_ alone acted, and this, as it related to the surrounding air, was rendered ineffectual by artificial temperature. The animals, therefore, could only be affected as to the temperature of the [p147] seasons _by that which preceded the experiments_. The modifications of the seasons, therefore, appeared to influence the cold-blooded animals used in the experiments in this point of view only. Accordingly we have this remarkable result, that the animals lived twice as long in autumn as in the summer preceding, when plunged in water of equal temperature. The _seasons_ evidently influence their constitutions, so as to extend the duration of life independently of other causes, that is, from summer to autumn. Dr. Edwards endeavoured to ascertain if it proceeds from atmospheric temperature, and he found that frogs lived in aërated water at ten degrees, during November, from five or ten to eleven, and even to forty hours, in some instances, the last term being about double the duration of life in water of the same degree in summer. This proves the remarkable dependence of the frog’s life under water, and the temperature of the month preceding. Two curious facts are thus developed by experiments instituted at different seasons. First, the influence of the temperature of the water in which the animals were placed; and secondly, the influence of the temperature of the air during certain periods preceding the experiments, for in autumn the duration of life was about double that of summer, and in winter he found the term to equal autumn, the temperature of the air being in each comparative experiment artificially raised to the same degree.

It appears from the foregoing experiments that frogs, toads, and salamanders, exist in water according to its _lowness of temperature_, and that their lives are prolonged _by the temperature which precedes the experiment being lowered_. It then becomes a question, what are the limits of this influence? This is to be ascertained by observing the greatest duration of life among animals deprived of external air by submersion in water; and noticing at the same time all the favourable circumstances dependent on the concurrent temperature in prolonging life among the cold-blooded animals.

A point relative to the natural history of frogs first presents itself to our notice. Spallanzani is of opinion that frogs do not pass the winter under water, but retire in October from their native rivers into moist sands, in which they make openings to breathe the air through, called by the Italian fishermen _il respiro della ranà_.

M. Bose, and other French naturalists, found that frogs retire from 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

The mean length of the seconds pendulum at the level of the sea, in the latitude of 45° 14′ 10″, deduced from these determinations, is 39.1154; and it is so equally, whether an ellipticity of 1/288th, or of 1/304th, or any intermediate ellipticity, be assumed in the reduction.

We have, then, 39.1154−39.0992 = ·0162 inch., as the [p158] measure of the difference in the intensity of gravitation at the place of observation elevated 1943 metres; and at the level of the sea. The radius of the earth, being 6,376,478 metres, this measure, according to the duplicate proportion of the distances from the earth’s centre, should be ·0238 inch. The attraction of the mountain is, then, equal to ·0238−·0162 = ·0076 inch. Whence it appears that, in this particular instance, the correction for the elevation is reduced, by the attraction of the interposed matter, 68/100ths, or to about 7/10ths of the amount immediately deducible from the squares of the distances.

It is obvious that, if we possessed a correct knowledge of the density and arrangement of the materials of which Mont Cenis is composed, so as to enable a computation of the sum of all the attractions which they exercise on the place of observation, this result might furnish, as well as Dr. Maskelyne’s experiments on the deviation of the plumb-line produced by the attraction of Mount Schehallien, a certain determination of the mean density of the earth. Professor Carlini considers that the form of the eminence may be sufficiently represented by a segment of a sphere, a geographical mile in height, having as its base a circle of 11 miles diameter, the distance from Susa to Lansleburgo; the attractive force, on a point placed on the summit, would, in such case, be equal to 2 π δ (1 − (2/3) √(1/11)) or in numbers to 5·020 δ, δ being the density of the mountain, and 2 π the ratio of the circumference to radius. The attractive force of the earth, on a point at its surface, is (4/3) π r Δ, = 14394 Δ, _r_ being the radius of the earth = 3437 geographical miles, and Δ its mean density. Now these two quantities, 14394 Δ and 5·020 δ, should be, to each other, in the proportion of 39.1154,—the pendulum at the level of the sea, representing gravitation at the surface of the earth,—to ·0076, the portion of gravitation at the summit of the mountain due to the attraction of the mountain. By the observations of M. de Saussure and other geologists, Mont Cenis is chiefly composed of schistus, marble, and gypsum; the specific gravities of which substances were ascertained, from numerous specimens in the possession of M. Carlini, to be respectively as follows:— [p159]

The schistous 2·81. The marble 2·86. The gypsum 2.32.

In the absence of a precise knowledge of the quantity and position or each of these three component parts, we may take the mean, 2.66, of their several densities as approximatively the density of the mountain, = δ. We have then

5.02 δ × 39.1154
Δ = -------------- = 4.77,
14394 × ·0076

a result differing little from that of Cavendish as recently corrected by Dr. Hutton, and still less from that of the Schehallien experiments.

The most hypothetical element of this calculation is the width assigned to the base of the mountain; but by the very nature of the question, it has but little influence on the final result; since, by even doubling the assigned diameter, the total attraction would not be altered a twentieth. In regard to the mean density of the mountain, if it were taken at 2.75, instead of 2.66, that of the earth would result 4.94, instead of 4.77, as given above.

E. S.

_Transactions of the Horticultural Society_. Vol. vii. Part 1. 4to. London, 1827. pp. 208.

I. _Observations upon the Growth of Early and Late Grapes under Glass_. By Mr. James Acon.

Few gardens are to be found in which bunches of fresh ripe grapes can be gathered every day in the year: notwithstanding the importance of the fruit to the luxurious, and the facility with which the vine submits to the artificial climate of the forcing-house. Nothing is easier than to secure crops of grapes in a vinery during the spring and summer months; but it is far more difficult to obtain them in the last and earliest seasons of the year, when the plants would [p160] naturally be in state of torpidity. It is well known that this desirable purpose is attained in great perfection in the garden of the Earl of Surrey, at Worksop Manor; and the management there practised is the subject of this paper.

The common methods of forcing early grapes are to train the vines under the roof near the glass, or on small frames against flued walls; but to both these practices Mr. Acon finds great objections: to the former because it renders the house too dark, and exposes the young and tender branches to the pernicious effect of blasts of cold air rushing through the interstices of the panes; and to the latter, because the heat of the flues is apt to scorch the branches, and in consequence to destroy the crop,—excessive heat in the one case producing the same injurious effects as excessive cold in the other. The following are the two modes by which Mr. Acon obtains his _very early_ and his _very late_ grapes. For the early crops a house is used, of which the back wall is 9.6 feet in height, and the front wall 3 feet, the roof forming an angle of about 30 degrees. It is heated, from the absolute necessity of employing an atmosphere of unusually high temperature, with two flues that pass along the middle of the house, and return in the back wall; a fire-place being built at each end of the house. Forcing begins on the first of September, and the fruit begins to ripen the first week in March. The vines are trained upon a trellis, fixed over the flues, in the centre of the house, and also upon the back wall; but none are allowed to obstruct the light by occupying the roof, until about six weeks after the forcing has commenced, when some new shoots are introduced and trained to the rafters. The form of this house gives it a peculiar advantage, in presenting a greater surface for the growth of vines than can be derived from any other plan; the trellis which is placed over the flues is nearly equal to the whole roof, without being in any degree injurious to the plants trained upon the back wall. The vines are planted in the inside of the house, but in such a manner that the mould in which they grow is not heated by the fire-places of either flue. The usual mode of exposing the main stem of a forced vine to an extremely low temperature in the external air, while the branches are stimulated by a very high temperature in an entirely different atmosphere, is very properly objected to. Nothing, in fact, can be more injudicious than such a practice, in cases where very early forcing is required; for it should be borne in mind, that although the absorption of the elements by which the proper juices of a [p161] plant are elaborated, and brought into the state under which they appear in the fruit, and in the secretions of the plant, is carried on by the leaves alone, yet that all these juices have, in the first instance, to pass along the vessels of the stem before they reach the leaves; and that the whole of the bark of a tree is, rightly considered, a leaf of a particular description, formed of the same kind of tissue, and exercising the same functions, and undoubtedly producing a powerful effect upon the motion of the fluids of the branches, with the vessels of which it is elaborately and intimately entangled, from the core to the circumference. No argument can be necessary to show that an equal action of the vessels of a plant is indispensable to the due maintenance of the vegetable functions in a healthy state, and that this is not to be maintained by exposing the main stem and the extremities to an atmosphere and temperature entirely different. Such irregularities do not exist in free Nature, and she will not submit to them when in fetters.

In pruning vines for early forcing, as little wood should be employed as possible. Mr. Acon stops the shoots one joint above each cluster, and has no joint without a bunch. When the crop is over, and the wood perfectly matured, the branches should be laid near the ground, and shaded till the recommencement of forcing. In short, they should be placed in a condition as nearly as possible resembling the gloom and cold of winter. If this process be well managed, the vines will alter their natural habits, and instead of budding with the spring, their vegetation will naturally commence at the period at which they have been accustomed to be stimulated.

For late grapes, a house of a different construction is employed. The back wall is 12 feet high, the front wall 1-1/2 foot, and the roof lies at an angle of 45 degrees. The heat is supplied by a single flue passing along the middle of the house. The sorts best adapted for late forcing are the Muscat of Alexandria, the St. Peter’s, and the Black Damascus; all other kinds wither prematurely. This house is generally shut about the middle or end of May, as soon as the bunches become visible. The vines are trained on a trellis near the glass. Till they are out of blossom the air is kept very warm, a point to which much importance attaches, because it is during this period that all the branches that are to bear fruit in the succeeding season are produced. In a high temperature, the branches will grow more compactly, and [p162] will be more regularly matured than in a low temperature, in which the wood is apt to become excessively luxuriant, and not to ripen well. Great attention must be paid to this point. As much air as possible is introduced into the vinery during the summer; but as the autumn advances, more caution in this respect is observed. The fruit should be perfectly coloured at the approach of the dark season; for if the colouring be deferred too long, the berries will never acquire their proper flavour. Great care must be observed to remove daily such berries as are inclining to damp, or the whole crop will soon be spoiled. This should be particularly attended to; for the contagion of what gardeners call _damp_, arises from the growth of minute fungi which vegetate upon the epidermis, and spread during the autumn with alarming rapidity from bunch to bunch.

The pruning of vines for late forcing is the same as has been already explained. When the crop is gathered, the house is unroofed for a short time, in order to expose the branches to a low temperature, and to the degree of humidity necessary to replenish their vessels, which have been drained by the dryness of the climate in which, when forced, they were necessarily kept.

By the means above described, a regular supply of grapes is secured through the year. The late-house crop lasts from the middle of January to the end of March; it is succeeded by the first crop in the early-house, which carries on the supply into May, and it is continued by the grapes on the rafters in the same house until the vines in the pine stoves, which are forced early in January and February, produce their crops. These continue bearing through the summer, when a vinery, of which the forcing commences about the end of March, furnishes the supply till the late-house fruit is ready in January.

Upon the whole this may be considered a most instructive and valuable communication.

II. _On the Varieties of Cardoon, and the Methods of cultivating them_. By Mr. A. Mathews.

Who does not wish to read of the cardoon; of that prince of vegetables, whose praises have been sung or said by all cooks and gourmands, from the fastidious Périgords and Cardellis of the French _cuisine_, down to the more homely Rundells and Glasses of our English kitchens; whose virtues are so marvellous as to be credible upon no less authority [p163] than that of the sage gastrophilists aforesaid. To restore unwonted vigour to old age, and new elasticity to youth, are the most modest of its attributes; the magical broth with which the veins of Æson were replenished by the cunning Medea, was doubtless prepared from the cardoon; and the story itself is probably a sort of figurative record of the skill of the fair enchantress in cooking this delicious vegetable, which was well known to the Grecian gastronomes under the name of κακτος; but this we throw out merely as a suggestion. Upon preparing herbs thus potent for the table, cookery has exhausted all its skill; to dress a cardoon is declared, by the highest authority in the art, to be the surest test of a skilful cook; and one of those invaluable acquirements which, to borrow the words of a writer not less celebrated for his powers of composition than of cooking, “raises cookery to the rank of the _sciences_, and its _professors_ to the title of artists.” Our good forefathers, indeed, “could not find the true manner of dressing cardoons,” and were content to eat them raw “with vinegar and oyl, pepper and salt, all of them, or some, as every one liketh for their delight;” which, considering that this vegetable is both bitter and astringent in a high degree, does not argue much for the delicacy of palate of our ancestors; little did they dream of the savoury preparations that modern art has devised by the aid of Espagnole, consommé, blancs, tammies, marking, masking, and all the mysteries of the stew-pan.

Four varieties are here described, of which the Spanish cardoon is the most common, and the cardon de Tours the best.

They are cultivated, like celery, in deep broad trenches, well manured and watered. When the plants are nearly full-grown, which will be about the end of October, a dry day is to be chosen for performing the operation of blanching them, which is thus effected:—

“The leaves of each plant are carefully and lightly tied together with strong matting, keeping the whole upright, and the ribs of the leaves together. The plant is then bound closely round with twisted haybands, about an inch and a half in diameter, beginning at the root, and continuing to about two-thirds of its height. If the plants are intended for winter store, they must be earthed up like celery; but if to be consumed before the frosts set in, the operation of earthing up may be omitted.” [p164]

III. _Accounts and Descriptions of the several Plants belonging to the genus Hoya, which are cultivated in the garden of the Horticultural Society at Chiswick_. By Mr. James Traill.

The beauty of one species of Hoya, viz., H. _carnosa_, has long caused it to be a favourite with collectors. The object of the writer of this paper is to call attention to such others as are known to exist in gardens, or as are preserved in the records of the botanist.

The following species form the subject of the paper, viz.:

1 Hoya carnosa, _R. Brown_. 2 Hoya crassifolia, _Haworth_. 3 Hoya pallida, _Lindley_. 4 Hoya Pottsii, (Tab. I.) 5 Hoya trinervis.

These five are all the species at present cultivated in gardens; others are known to exist in the warmer regions of Asia, where they should be assiduously sought for by travellers, as they are not only very ornamental, but easily to be transported to Europe.

From such materials as he has been able to procure, the writer enumerates the following as completing the genus Hoya, as far as at present ascertained:

6 Hoya chinensis. 7 Hoya viridiflora, _R. Brown_. 8 Hoya lanceolata, _D. Don_. 9 Hoya linearis, _D. Don_. 10 Hoya australis, _R. Brown_, _MSS_. 11 Hoya nicobarica, _R. Brown, MSS_. 12 Hoya augustifolia.

The paper concludes with a detailed explanation of the best manner of cultivating Hoyas.

IV. _On acclimatizing Plants at Biel, in East Lothian_. By Mr. John Street, gardener to the Honourable Mrs. Hamilton Nesbitt.