particles may well be said to be squeezed out of the sounding substance, by the percussion and the consequent agitation. The analogy between the globules of sound and those of the electric or gal, vanic fluid, are most striking in their action in vacuo, and, indeed, in every other way, including the laws of chemical affinities and even of animal life. But I must leave my remarks on this interesting subject to another and more especial disquisition. By-the-bye, I have often been struck by the singular humming, buzzing, singing noise with which we are assailed upon plunging over head and ears in water, and particularly in diving to a considerable depth into the sea." Through the aid of a heavy iron weight, I have plunged to the bottom of the sea, to a depth of eighty-six feet. On such occasions, the internal noise I allude to, is particularly loud and various. Now I am inclined to attribute it to the different motions and frictions of our muscles, blood, heart, intestines, eyes, and even brain, giving out different sounds which are compressed and concentrated by the surrounding and superjacent wa

ON THE SOURCE OF ELECTRICITY AND ITS ACTION ON PLANTS IN THEIR MATURING PROCESS.

Sir, In what has been advanced by me upon the subject of electro-vegetation in your pages, I trust it will have been perceived that there has been a constant endeavour to avoid mere theory, and to build as much as possible on facts. Still as several general positions have been stated which differ, in terms at least, from those which have been laid down in treatises, and as some of them cannot pretend to a higher support than that of probability, I feel that in proceeding to such considerable lengths, I am treading on tender ground. But I write under the persuasion that truth, or some near approaches to it, ordinarily presents itself under the form of probability, before it can have been sufficiently investigated to determine its certainty; nor can I help

thinking that as human nature is ever prone to exrtemes, so that of caution in the bare announcement of facts, without attempting to advance a step farther than the facts seemed absolutely to demonstrate, has imposed a restraint on the bounds of probable truth, which has ope rated to some extent in precluding the steps towards its more certain and exact attainment. This restraint upon the operations of the mind seems moreover to have been attended with another unfavourable result of an opposite description for its propensity to generalise, breaking through its preternatural bonds, appears to have led to several hasty con clusions, both of a negative and positive description. Thus it has been laid down as so many established positions, that light, heat, and electricity, are not differ- [ ent effects or phenomena, attendant on the operations of one imponderable, alldiffusive, fluid, but of three or even four different fluids of this description; although it cannot be denied that they are frequently observed under circumstances of such intimate connecxon, that they have every appearance of proceeding from one uniform cause. Indeed, it seems next to impossible to observe the powerful electrical effects resulting from the arrangements of a galvanic battery, ac- companied with a corresponding inten sity of heat, and a light more nearly approaching that of day than can be pro duced by any other artificial means, without concluding, for the moment at least, that they are different effects produced by the operations of the same fluid, which is thus drawn from its general diffusion through gravitating matter, and concentrated to one spot. In like manner, when we observe light and heat issuing from the sun, and diffused through the atmosphere under every appearance of a common result of the same fluid proceeding from one source, we seem almost unavoidably led to the inference of their common origin and nature. We do not, indeed, find them always united, at least in an equal degree; but may not this circumstance admit of an easier explana tion from regarding them as different effects produced by the same fluid in whose operations they are so often seen to be closely united, than by viewing them as absolutely separate and distinct in their essential properties? Do we not often perceive light becoming latent

*

*

under the form of caloric, and again set at liberty in the form of both light and heat? We do not observe electri cal effects to be the usual or very frequent effects of the fluid issuing from the sun; but a dry air, over which the sun's rays are dispensed, is now well known to be in a constant state of positive electricity. The air, in its relation to the sun, may justly be compared to a great electrical machine, which is constantly receiving its supplies from above, and either imbibing them into its substances, or transmitting them to the earth and its vegetable productions, through the medium of those exquisite conductors with which they are furnished. That these effects are so little open to our observation is not because electricity, or the fluid by which it is produced, is not very extensively dispensed in nature, has recently been shown in a striking manner by that ingenious practitioner, who has collected it in such formidable and effective states by means of wires extending through the atmosphere. But whereas the efforts of art are directed to collect it at particular spots, those of nature are almost uniformly directed to the opposite purpose of dis pensing it in those regular and nearly imperceptible quantities, which are at once essential to maintain the existence and preserve the harmony and tranquillity of the system. It does appear with considerable evidence that light, heat, and electricity, are continually dispensed into our atmosphere from that great central body, which is perhaps equally necessary to the repellant as to the gravitating properties of the planetary bodies. It is surely evident that, since myriads of conductors fitted to imbibe electricity from clouds at elevations on which metallic points can have no influence, every where shooting up from the surface of the earth, are insufficient to prevent a constant state of positive electricity in the atmosphere, supplies of this fluid must be as constantly administered to it from above as of light and caloric; and from whence can these continual supplies of electric matter proceed but from the same common source? But that divine skill which regulates the quantities and manifestations of light and heat, and of the principle of expansion in those proportions which are requisite or conducive

*Andrew Crosse, Esq.

to life and enjoyment, is applied in causing the electrical operations of the same fluid to proceed almost imperceptibly in producing many other effects, no less essential or conducive to the same results.

There is reason to believe that the third and concluding process of vegetation to which we shall now immediately attend, is influential in a far greater degree in carrying forward this design than either of the preceding processes. As the solar beams increase in number and intensity, vegetation advances; its branches extend and send forth innumerable ramifications, and its leaves, in a manifold greater numeral proportion, expand into palmated shapes of a porous structure, fitted for the reception of immense quantities of light, and furnishing continual supplies of water, which, by combining with it in the state of transparent vapour, neutralizes their action, and makes provision for a sheltering canopy over our heads, adn for a seasonable supply of moisture both upon the soil and plants. As animal life also of every kind is now rapidly advancing, and oxygen gas is by the action of the respiratory organs rapidly exchanged for carbonic acid, the leaves of plants appear to be now constantly engaged in the function of absorbing this deleterious gas, which, with the returns of light, is reconverted into pure oxygen air; and thus another great and essential benefit to both the animal and vegetable systems is effected. The presence of carbonic acid is essential to plants; "it has been ascertained that feed plants, as you will, they will neither grow nor live, whether you offer them oxygen, hydrogen, or azote, or any other gaseous or fluid principle, unless carbonic acid is present."+ It is evidently decomposed by the action of light, the carbon remaining in the substance of the leaves, or uniting with the descending portion of the sap, while the oxygen retaining the gaseous form is restored to the atmosphere.

I flatter myself it will have appeared from the above and the foregoing statements, that the three processes which have been assigned to vegetation, corresponding with the principal elements of the atmosphere, are attended with considerable evidence. If its action in each of these processes is electrical, in proof of which,

+ Prout on Chemistry, p. 451.

facts and experiments have been adduced in each instance, it appears to follow that electricity is the great principle by which vegetation is carried forward. And as they apply severally to air, vapours, and light, they manifest the existence of this principle in each of those elements. Now, if it is found floating in an uncombined state in the air; if by its being extracted from vapours they are reduced to a liquid state; and if in the form of light, it performs the galvanic effect of decomposition, is not strong direct evidence afforded that the same solar fluid is manifested under the three forms of light, heat, and electricity? If this be admitted, it appears to me that considerable light will be thrown upon this system of nature, and the relation between plants and animals. The

sensible effects of electricity are in general disagreeable and injurious; they are, however, we conceive, no other than the effects of the solar fluid floating in a state of separation from gravitating matter, and seeking to obtain an equable diffusion among its particles. A small quantity of it alighting on solids, especially if they be non-conductors, quickly assumes the form of electricity, as it cannot enter their pores and separate their closely united particles with sufficient facility to become latent within their substance. If in the form of light it strikes the surface of water, it easily combines with a small portion of it in a state of vapour; and its electrical properties are thus neutralised. By impingeing upon the earth, and being reflected into the atmosphere, a greater or less degree of electricity is probably produced, especially if the surface of the earth is dry; but the effect is greatly alleviated by the readiness with which the air, in common with all gaseous bodies, opens to receive the fluid in the form of a moderately increasing temperature and rare.. faction. According to these views, there is an increasing necessity for neutralising the action of the solar beams to a certain extent; or of diverting their operations from the forms of light, heat, and electricity, as the summer season advances, to some other necessary and useful purposes. And these purposes appear to be effected by the increasing foliage of plants. The moisture upon the surface of the soil being quickly evaporated, there is the greater necessity for that copious supply of moisture which is constantly yielded under the action of light from the leaves and even

the green stems; and every particle which is thus rendered latent in the form of aqueous gas, diminishes the quantity of sensible heat and the glare of light which would otherwise remain in the atmosphere.

66

But we also find that a process of greater and more absolute necessity, both to the animal and vegetable systems, is going forward at the same time, though in a less perceptible and more gradual manner, by means of a similar action of the solar beams upon the carbonié acid, of which these organs are the constant absorbents. It is by means of these concurring properties of the leaves, and of the light acting upon them, that we are ena bled to account for a large portion, at least, of the carbon which we find entering into the substance of plants, and of the oxygen gas by which the vital princi ple is maintained in animals. It is an observation of Sir H. Davy, that we know of "no process in nature by which the carbonic acid formed during fermentation, combustion, putrefaction, respiration, and a number of operations taking place on the surface of the earth is destroyed, but by vegetation." "When," he observes, a growing plant, the roots of which are supplied with proper nourishment, is exposed in the presence of solar light to a given quantity of atmospherical gas, containing its due proportion of carbonic acid, the carbonic acid, after a certain time, is destroyed, and a certain quantity of oxygen is found in its place. If new quantities of carbonic acid be supplied, the same result occurs; so that carbon is added to plants from the air, by the process of vegetation in sunshine; and oxygen gas is added to the atmosphere. This circumstance is proved by a number of experiments made by Drs. Priestley, Ingenholz, and Woodhouse, and M. T. de Saussure, many of which I have repeated with similar results." I have been induced to add these extracts from Sir H. Davy's observation in conformation of my former statements, both on account of the importance of the principle they advocate, and the beautiful harmony which it presents between the functions of plants and animals, and because it still appears a prevailing opinion of physiologists, that vegetables are almost identified with ani

mals with regard to their respirative and their digestive functions. In page 453, of the same work, from which the above short extract on the necessity of carbon to the growth of plants is made, it is said, on the authority of Professor Burnet, that the process of respiration in plants is supposed to be continual, and to be accompanied, as in animals, by the formation and emission of carbonic acid gas." It is admitted, however, that during their exposure to the light of the sun, the decomposition of this gas from the atmosphere, and the absorption of the carbon from the acid is effected. In other words, carbonic acid is removed from the atmosphere, and oxygen gas is produced. It is surely an extraordinary "supposition" that plants are giving out carbonic acid to the atmosphere at the same time, and under the same circumstances, in which it has been clearly proved, that they are effecting its removal. But this last is ascribed to "the process of digestion" in plants; whereas a separate process of respiration, it seems to be taken for granted, must also be carrying forward; but to identify plants with animals, and from that hypothesis to make a supposition in opposition to a fact clearly proved and admitted, is a mode of proceeding not very congenial with the true spirit of philosophy.

We trust it has been proved that plants, instead of continually emitting carbonic acid, are imbibing it by their leaves as continually as it is exposed to their action; a process which indeed seems essential to the aggregation of that large proportion of carbon which enters into their composition; and with which the supposition of their being subjected to the continual loss of carbon by an opposite process is utterly irreconcilable. In truth, the analogy, or rather identification, which is sometimes represented as existing between plants and animals, with respect at least to their digestive and respiratory functions, appears to have much less foundation in reality than has been imagined. What strong marks of resem blance are there between the most perfect of the orders of animals, and the most perfeet of the vegetable tribes? Or with what degree of correctness can the favourite comparison between the lungs of an animal and the leaves of a plant be maintained? The former are admirably constituted for the purpose of admitting

large supplies of air into their expanded vesicles; of receiving from it that supply of caloric which is necessary to the uniform heat and vitality of the animal; and at the same time, of transmitting to the oxygen a portion of carbon, which, if retained in the blood, would impede its circulation. The leaves of plants, on the contrary, from their origin in buds to their full expansion, manifest no such property. In proof of this position, I have made several experiments with seeds growing under the receiver of an air-pump carefully kept in a state of exhaustion; from which I think myself fully justified in the assertion, that cresses and mustardseed at least will germinate, grow, and flourish, in a state of exhaustion, in which any of the more perfect orders of animals, those especially which live by means of well-developed organs of respiration, would almost instantly perish. We have in the foregoing papers endeavoured to show that plants derive the vital principle not by a respiratory process, but by that electric action on the air and vapours for which their whole structure, and particularly their pointed and edged extremities, are so admirably calculated. This property they no doubt continue to exert so long as they retain these conducting organs in a state fitted for action; and the enlargement of the plant with its increasing foliage must extend its electrical influence. But as the growing stage of its existence passes into that of maturity, we have seen that a different process is going forward to an increasing extent; the leaves become fully developed, but we repeat our statement, that from every observation we have been enabled to make, as confirmed by those of the great names to which we have appealed, these effects with respect to carbonic acid are the reverse of those which are produced by animal respiration. In my fourth letter on electro-vegetation, I have stated the experiments by which I unexpectedly was led to the conviction, that leaves imbibe carbonic acid with avidity in the absence of light, and during the night season, and which, as they consist simply in placing leaves, or sprigs of leaves, whether on the trees, or immediately after they have been plucked, in water or air containing a small quantity of carbonic acid, too large a quantity proving deleterious, can easily be re

peated. It being also known that they perform the same function under the action of light, when oxygen gas is extracted, the conclusion appears indubitable that the function of the expanded leaf is, in this respect, the reverse of that of animal respiration, consisting in the absorption of carbonic acid, both by night and day; while under the influence of light it emits pure oxygen gas to the atmosphere.

If the principles which we have advocated be founded in fact, vegetation is, in every point of view, and by means of its several effects upon the surrounding elements, conducive to the existence and welfare of the animal creation. It derives its vitality from the same solar fluid as that by which the animal heat and life is maintained. But it is drawn by elastic action from those portions of it which floating on the air, or set loose by condensing vapours, would otherwise either augment the quantity of electricity or of heat in the atmosphere in excessive degrees. Carbon, forming a large portion of its nutriment, and an essential of its existence, is imbibed by it in its connexion with oxygen apparently in a like proportion to that in which it is given out by the several opposite processes, and in particular by animal respiration. By this process, in connexion with that of evaporation, it is eminently conducive to the existence and well-being of animals, during the period of its greatest vigour and luxuriance; as by these means the solar fluid is combined with oxygen in a state of fitness for maintaining their vital principle; or by combining with water, a cooling shade is formed in the atmosphere and by both these processes, but especially by the latter, great quantities both of heat and of electricity are prevented from accumulating in it.

of subsistence, comfort, and enjoyment in other respects. As it produces compounds from bare elementary bodies suited for the food of animals, so it produces a compound of air exactly suited to their respiratory organs. And thus, in a scale gradually ascending from elementary and inorganised matter, the inferior orders of beings and of substances are made subservient to the higher. ST. PINE.

In the forming of these conclusions, facts have either preceded or gone hand in hand with theory, but I hope that many of your readers will concur in the sentiment, that the

PERPETUAL MOTION.

Sir, From the tone of Nautilus's reply, I am afraid he is losing his temper. If he be really in search of truth, he will succeed all the better, I think, by proceeding coolly, and his observations would have more weight too, if he were to deliver them in language a little more respectable than he has employed in his last. He says, "as for the assertion that Kinclaven has been knocked on the head with the lump of lead on the arm of the fly-wheel, I leave it to himself to deny it; I can find no marks of the dent in any of his letters." Now it may be true that Nautilus cannot perceive the dent, and yet there may be a very deep dent, notwithstanding; all persons are not gifted alike with the faculty of perception, and, as he very candidly confesses his dulness, it may not be thought uncharitable to give him a little aid on this occasion. Well, Nautilus, Kinclaven commenced his attack upon the electrical theory, by announcing, in the most confident terms, that the Newtonian system had been rigidly demonstrated, and that therefore the electrical theory must false. He was meekly reminded of two propositions that have not yet had the benefit of any demonstration whatever, although they happen to be the very two upon which the whole system depends, and was respectfully solicited to supply this deficiency before he said any more about the "rigid demonstrations." Kinclaven,

be

considerably to confirm the credibility of the general results. Upon the principles we have advocated, vegetation stands in a corre sponding state of subordination and sub. servience to the animal system as it respects the means of vitality, and the general temperature and tranquillity of the atmosphere, that it does to the means

predicament, has very kindly referred me to the parson for one of the demonstrations, which he says is to be, not of the mathematical, but of the orthodox kind; as for the other, Kinclaven keeps it in imo pectore, as Nautilus says, in reference to the perpetual motion problem. Here then, Nautilus, are two very plain dents, but if they are still imper