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 On the CAUSE of the VARIATION of the NEEDLE.
and by the decompofition of iron; and, laftly, that it is probably annihilated by a very great degree of heat.
"These truths being premifed, it must be confidered, firit, that, according to innumerable obfervations and daily experience, the body of the earth contains almoft every where ferruginous bodies in various ftates and bulks. Secondly, that the magnetic needle must be attracted by all those bodies, and its fituation or direction must be determined by all thofe attractions confidered together, viz. from their common centre of action. Thirdly, that by removing or altering the degrees of attraction of fome of thofe bodies, which are fituate on one fde of the magnetic meridian, more than of thofe fituated on the other fide, the above-mentioned common centre of attractions, and, of course, the direction of the magnetic needle, must be altered, which, in fact, is the variation of the needle. And, laftly, that this alteration in the attractions of fome of the ferruginous bodies in the earth muft undoubtedly take place, it being occafioned by the parts of the earth being irregularly heated and cooled, by the action of volcanos, which decompofe or otherwife alter large mates of ferruginous fubtance; by earthquakes, which remove ferruginous bodies from their original places; and we may add alio by the aurora borealis; tor though we are as yet ignorant of the caufe of that furprising phenomenon, it is, however, certain, that the magnetic needle has been frequently disturbed when the aurora borcalis appeared very strong.
"The magnetic needle, therefore, being neceflarily affected by
thefe caufes, and they appearing fufficient to account for its variation, it feems unneceffary to have recourfe to other hypothetical caufes, which are not established on actual expe. rience.
"In order to exemplify this explanation of the variation in a familiar manner, I made the following experiment:-Four earthen veffels were difpofed round the mag. netic needle, two near its fouth, and the other two near its north pole, but not at equal distances. In one of thofe veffels there was placed a natural magnet; the fecond contained feveral fmall bits of magnetic feel mixed with earth; and in each of the other two there were put about four ounces of iron filings. Things being thus difpofed, and left undisturbed for about half an hour, the needle remained unaltered. Then the pieces of magnetic fteel and earth were firred with a flick, in confequence of which the needle was agitated. Af ter this, fome diluted vitriolic acid was poured upon the filings in one of the veffels, the action of which attracted the needle that way; but whilst the needle remained in that fituation, fome diluted vitriolic acid was poured upon the iron filings in the other veffel, which flood on the other fide; in confequence of which the needle went back again towards its former direction. Whilft the effervefcences were going on in the two veffels, the magnet in the first veffe was heated by means of buil ing water, which occafioned another alteration in the direction of the magnetic needle; and thus, by altering the state of the ferruginous fubftances in the veffels, the needle's direction was altered, in evident imitation of the natural variation."
On the PERCEPTIBILITY of VEGETABLES.
[From the Fifth Volume of Dr. WATSON'S Chemical Effays.]
VERY one thinks that he knows what an animal is, and how it is contradiftinguifhed from a vegetable, and would be of fended at having his knowledge que ftioned thereupon. A dog or a hotfe, he is truly perfuaded, are beings as clearly diftinguifhed from an herb or a tree, as light is from darknefs; yet as in thefe, fo in the productions of nature, the tranfition from one to the other is effected by imperceptible gradations.
"The loco-motive powers which appertain to moft animals, whether they proceed from the Cartelian mechanifm, or from fenfation, are fo manifeft in quadrupeds, birds, fithes, and infects, that in our firit and fuperficial inquiries into nature, we are apt to confider the poffeffion or want of these powers, as making a decisive and effential difference between animal and veget. able bodies; and it is not without a certain degree of regret, as it were, that we find ourselves obliged to predicate animality concerning a great varity of beings, which are deftitute of every power of progreffive motion. If at the fame time we happen to have entertained fome preconceived opinions, no matter whence they have been derived, concerning the ufual fhapes of animals, (though they are far more different from one another than fome of them are from vegetables) our repugnancy to the admitting a being of the outward form of a fhrub, into the clafs of animals, is much increased. Hence have proceeded most of the objections which have been made to the fine difco. veries of Peyflonel, Juffieu, Eilis,
and others, relative to the animal nature of corals, madrepores, millepores, corallines, fpunges, and a numerous tribe of bodies which the very ingenious labours of Marligli had formerly removed from the mineral kingdom, where they had been placed by Woodward and other mineralifts, and allotted to that of vegetables.
"If rejecting fpontaneous motion and figure as very inadequate tetts of animality, we adopt perception in their ftead; no doubt, he would be efteemed a vifionary in philofophy who fhould extend that faculty to vegetables; and yet there are feveral chemical, phyfical, and mataphyfical reafons which feem to render the fuppofition not altogether indefenfible.
"The greater the quantity of perception exifting in the univerfal fyftem of creation, the greater is the quantity of happiness produced; and the greater the quantity of happinefs produced, the greater is the goodnefs of the Deity in the ettimation of beings with our capacities. The latter part of this propofition needs no proof; and the former is liable but to one objection, and that grounded upon a falfe fuppofition. If, it may be urged, all the fpecies of percipient beings be not accommodated with objects, congruous to their faculties of per ception, and productive of more pleafure than pain to the whole fpecies taken collectively, then the animation of that matter of which they confift is an introduction of evil, and no teft of benevolence. This may be granted; but in all the species of beings which come
within the obfervation of our fenfes, the fuppofition of their not being furnished with objects fuited to their well being is evidently not true, and therefore ought, from analogy, to be rejected with reference to fuch as by their magnitude, their minuteness, or their duinefs of perception escape our examination.
That animals fhould feed one upon another, is a law of nature full of wifdom and goodnefs, life and happinefs being indefinitely multiplied thereby. For a given quantity of what are called veget. ables, annually produced upon a globe of a given diameter, being fufficient but for the fupport of a given number of herbaceous animals, whofe place in the univerfe not admitting their immortality, it hath been wifely contrived that their bodies, which from their structure mult perish, should in ceafing to live, become the inftruments of fupporting life in beings, which could not by any other means have had an existence, at least upon this globe; and of the other parts of the universe we know nothing except from analogy, and from that we must conclude that the rò a, be it finite or infinite, is as full of life as this particular part with which we are connected. Nay, animated matter, containing as it were the concentrated virtue of many vegetables, ferves for the fup. port of life, and the confequent communication of happiness in a far more ample manner than vegetables themselves; animal fubitances in equal weights furnishing more nutiment than vegetable. It is by death a feeming imperfection in his workmanship, that the Deity preferves vegetable life, fupports the animal kingdom, daily regulates and renews the economy of nature, and continues this wonderful fyftem
of things in full youth and vigour, not interrupted by difeafe, nor enfeebled by old age.
"No objection therefore to the animality of vegetables can be brought from any confiderations refpecting their daily deftruction'; for the cedruction of animals by other animals, the bellum omnium in omnia, is an univerfal law of nature, derived from the fame benevolence to which we attribute creation itfelf. If then every part of the vegetable kingdom hath a degree of percep ivity, however fmall, there will be a gain of happiness to the whole fyllem; the aggregate may be of a value not to be overlooked by him, to whom the existence of all things is equally poffi. ble, and from whom all created exiftences are equally distant in perfection.
"Wherever there is a vafcular fyftem, containing a moving nutritive fuccus, there is life; and whereever there is life there may be, for aught we can prove to the contrary, a more or lefs acute perception, a greater or less capacity for the reception of happiness: the quantity, indeed, of which after we have defcended below a certain degree of fentibility, will (according to our method of eftimating things, which is ever partial and relative to ourselves) be small in each individual; yet is the exiftence of it in the nature of things poffible, from the analogy of nature probable: and who can tell whether in a fyftem of nature, confeffedly contrived for the production of the greateft poffible good, it may not. alfo be neceffary?
"It should be well weighed by the metaphyficians, whether they can exclude vegetables from the poffeffion of the faculty of perception, by any other than compara
tive arguments; and whether the fame kind of comparative reafoning will not equally exclude from animality thofe animals which are provided with the fewest and the obtufest senses, when compared with fuch as are furnished with the most and the acuteft. The perception of a man (though it may be doubted whether there are not feveral animals which have all the fenfes more acute) teems to be indefinitely greater when compared with that of corallines, fea-pens, and oyfters, than the perception of thefe, which are allowed to be animals, doth when compared with the figns of perception manifefted by a variety of what are called vegetables. Spunges open and fhut their mamilla, corals and fea-pens protrude or draw back their fuckers, fhellfifh open or keep clofe their fhells in fearch of food or avoidance of injury; it is from thefe and fimilar mufcular motions that we judge the beings to which they belong to have perception, that is, to be animals. Now in the vegetable kingdom, we may obferve the muf. cular motions of many plants to be, to the full, as definite and diftinguishable as thofe of the clafs of animals just mentioned. The plants called heliotrope turn daily round with the fun; by conftantly prefenting their furfaces to that iuminary, they feem as defirous of abforbing a nutriment from its rays, as a bed of mufcles doth from the water, by opening their thells upon the afflux of the tide. The Flores Solares are as uniform in their opening and shutting as animals are in their times of feeding and digeft ing; fome in thefe motions do not obferve the feafons of the year, but expand and fhut up their flowers at the fame hour in all feafons; others, like a variety of infects
which appear, or not, according to the heat of the weather or climate, open later in the day, or do not open at all, when they are removed from a fouthern to a more northern latitude. Trefoil, wood-forrel, mountain ebony, wild fenna, the African marigold, &c are fo regular in folding up their leaves before rainy weather, that they seem to have a kind of instinct or forefight fimilar to that of ants; which however deferts many of them as foon as they have propagated their kind, by fhedding their pollen. Young trees, in a thick forett, are found to incline themselves towards, that part through which the light penetrates, as plants are obferved to do in a darkened chamber towards a ftream of light let in through an orifice, and as the ears of corn do towards the fouth. The roots of plants are known to turn away with a kind of abhorrence from whatever they meet with which is hurtful to them, and to defert their or dinary direction, and to tend with a kind of natural and irresistible impulfe toward collections of water placed within their reach: many plants experience convulfions of their ftamina upon being flightly touched. Whatever can produce any effect upon an animal organ, as the impact of external bodies, heat and cold, the vapour of burning fulphur, of volatile alcali, want of air, &c. are found to act allo upon the plants called fenfitive. But not to infift upon any more inftances, the mufcular motions of the Dionea Mufcipula, lately brought into Europe from America, feem far fuperior in quickness to those of a variety of animals. Now to refor the mufcular motions of fhell fish, and zoophytes, to an internal principle of voli ion, to make them indicative of the perceptivity of the
being; and to attribute the more notable ones of vegetables, to certain mechanical dilatations, and contractions of ports occafioned by external impulfe, is to err against that rule of philofophyzing which affigns the fame caufes for effects of the fame kind. The motions in both cafes are equally accommodated to the prefervation of the being to which they belong, are equally diftin&t and uniform, and fhould be equally derived from mechanifm, or equally admitted as criterions of perception.
"I am fenfible that these and other fimilar motions of vegetables may by fome be confidered as analogous to the automatic or involuntary motions of animals; but as it is not yet determined amongst the phyfiologists, whether the motion of the heart, the peristaltic motion of the bowels, the contractions obfervable upon external impulfe in the mufcles of animals deprived of their heads and hearts, be attributable to an irritability unaccompanied with perceptivity, or to an uneafy fenfation, there feems to be no reafon for entering into fo obfcure a difquifition; efpecially fince irritability, if admitted as the caufe of the motions of vegetables, muft, a fortiori, be admitted as the caufe of the lefs exquifite and difcernible motions of beings univerfally referred to the animal kingdom.
"Physical obfervations concerning the generation, nutrition, or ganization, life, health, ficknefs, and death of plants, help us as little towards the establishing a difcriminative characteristic between them and animals, as metaphyfical fpeculations relative to the quantity of happiness, or degrees of perceptivity.
"The eaftern practice of fœcundating the female palm tree by fhak
ing over it the dust of the male, which Herodotus mentions in his account of the country about Babylon, and of which Dr. Haffelquift in the year 1750 was an eyewitnefs, was not unknown to Ariftotle and Pliny: but the ancients feem not to have carried the fexual fyftem beyond that fingle inftance, which was of fo remarkable a kind, that it was hardly poffible for them to overlook it; at present there are few botanists in Europe who do not admit its univerfality. It feems generally agreed, that a communication of fexes, in order to produce their like, belongs to vegetables as well as to animals. The difputes fubfifting among the anatomists, concerning the manner in which conception is accomplished, whether every animal be produced ab ovo femella, or a vermiculo in femine maris, are exactly fimilar to thofe amongst botanists concerning the manner in which the farina fæ cundans contributes to the rendering the feed prolific: but however thefe doubts may be determined, they affect not the prefent inquiry, fince it is allowed on all hands, that as the eggs of oviparous animals, though they arrive at their full magnitude, are incapable of being. vivified by incubation, unless the female hath had commerce with the male fo the dates of female palm trees, and the fruits of other plants, though they ripen, and arrive at maturity, will not grow unless they have been foecundated by the pollen of the male.
"In like manner, notwithstanding the diverfity of opinion which hath long fubfifted, and in a matter fo little capable of being enlightened by experiment, probably ever will fubfift, concerning the modus agendi by which nature elaborates the nutritive fluid, admi