« AnteriorContinuar »
epitome of the essential characters of a species. Several duplicates of every species should be collected.
“ Preserving Specimens of Alga.—Where it is a collector's object to preserve algæ in the least troublesome manner, for the purpose of transmitting them to Europe, it is merely necessary to spread the specimens, immediately on being brought fresh from the sea, without any previous washing, and even without squeezing their natural moisture from them, in an airy situation, as hay is spread out to dry, only they must not be exposed to too powerful a sun. In dry weather, if the layer be turned over a few times, they will very rapidly dry, and no other preparation is necessary. They will have shrunk considerably, and many will have darkened in color, and the bundle may have become very unsightly; nevertheless, if thoroughly dried to prevent mouldiness or heating), and packed loosely in paper bags or rough boxes, such specimens will, generally speaking, reach Europe after many months, in a perfectly sound state ; and, on being re-moistened and properly pressed, will make excellent cabinet specimens. It is very much better, when drying algæ in this rough manner, not to wash them in fresh water, because the salt they contain serves the double purpose of preserving them, and of keeping them in a pliable state, causing them to imbibe water on re-immersion more readily. Washed algæ, roughly dried, become very hard and unmanageble. I would recommend that all the larger and coarser kinds of algæ, sent from abroad, be preserved in this manner. With the more delicate and smaller kinds, a different course may be pursued.
• Preserving delicate Alge.-Small, filamentous, and gelatinous algæ cannot be well preserved in the rough manner just described, and, when practicable, should be put up, after gathering, on the papers on which they are intended to remain. With a little care, and after a few trials, the mode of preparing them will be easily learned.
“ The collector should have two or three flat dishes, one of which is to be filled with salt water and two with fresh; in the first of these the specimens are to be rinsed and pruned, to get rid of any dirt or parasites, or other extraneous matter; they are then to be floated in one of the dishes of fresh water for a few minutes, care being taken not to leave them too long in this medium, and then one by one removed to the third dish, and a piece of white paper, of the size suited to the size of each specimen, is to be introduced underneath it. The paper is to be carefully brought to the surface of the water, the specimen remaining displayed upon it, with the help of a pair of forceps or a porcupine's quill, or any fine-pointed instrument, and it is then to be gently drawn out of the water, keeping the specimen displayed. These wet papers, with their specimens, are then placed between sheets of soft soaking-paper, and put under pressure, and in most cases the specimen in drying adheres to the paper on which it is laid out. Care must be taken to prevent the blotting-paper sticking to the specimens and destroying them. Frequent changes of drying-paper (once in six hours), and cotton rags laid over the specimens, are the best preservatives. The collector should have at hand four or five dozen pieces of unglazed thin calico (white muslin (such as costs five or six cents a yard), each piece about eighteen inches long and twelve wide, one of which, with two or three sheets of paper, should be laid over every sheet of specimens as it is put in the press. These cloths are only required in the first two or three changes of drying-papers, for, once the specimen has begun to dry, it will adhere to the paper on which it has been floated, in preference to the blotting-paper laid over it. Should it perversely adhere to the calico, it is better not to attempt to detach it till it is nearly dry, when by a little care it may generally be got free. Algæ do not take so long to dry as other plants, and many, in warm weather, will be found to be sufficiently dried after forty-eight hours, if the papers have been changed three or four times.
“Corallines, and Sponges, require no trouble when once collected; it is merely necessary to dry them roughly, and pack them among the rough-dried sea-weeds in boxes. As much interest attaches to these productions, and as those of tropical and sub-tropical countries are still very imperfectly known to naturallists, collectors of algæ are earnestly requested to secure them whenever they present themselves.”
ART. V.-Objections to the Theories severally of Franklin,
Dufay and Ampère, with an Effort to Explain Electrical Phenomena by Statical or Undulatory Polarization ; by RobERT HARE, M.D., Emeritus Professor of Chemistry in the University of Pennsylvania.
(Continued from ii Ser., vol. v, p. 351.) Process by which the Ethereo-ponderable Atoms within a Gal
vanic Circuit are polarized by the Chemical Reaction. 53. In order that an ethereo-ponderable particle of oxygen in any aqueous solution shall unite with an ethereo-ponderable particle of zinc in a galvanic pair, there must be a partial revolution of the whole row of ethereo-ponderable zinc atoms, with which the atom assailed is catenated by the attractions between dissimilar poles. Moreover, at the same time that the metallic atoms are thus affected, the atoms of water between the metallic sur
faces must undergo a similar movement, by an analogous reaction with poles of an opposite character, and this movement must extend through the negative plate to the conductor, by which it communicates with the zinc or electro-positive plate. When the circuit is open, the power of combination exercised by the zinc and oxygen is inadequate to produce this movement in the whole chain of atoms, liquid and metallic; but as it is indifferent whether any two atoms are united with each other, or with any other atoms of the same kind, the chemical force easily causes them to exchange partners, as it were, when the whole are made to form a circuitous row in due contiguity.
59. As we know that during their union with oxygen, metals give out an enormous quantity of heat and electricity, it is reasonable to suppose that whenever an atom of oxygen and an atom of zinc jump into union with each other, a wave is induced in the ethereo-ponderable matter, and that this wave is sustained by the decompositions and recompositions by means of which an atom of hydrogen is evolved, at the negative plate and probably enabled to assume the aëriform state. There must, at the same time, be a communication of wave polarity by contact of the negative plate with the connecting wire, by which the positive wave in the wire is induced. Although the inherent polarities of the metals are not, agreeably to this view, the moving power in galvanism, yet they facilitate, and in some cases induce the exercise of that power, by enabling it to act at a distance, when otherwise it might remain inert.
60. This, I conceive is shown in the effect of platina sponge upon a mixture of the gaseous elements of water; also in Grove's gas battery, by means of which hydrogen and oxygen gas severally react with water in syphons, so as to cause each other to condense, without any communication besides that through the platina, and an electrolytic decomposition and recomposition extending from one of the aqueous surfaces in contact with one of the gases, to the other surface in contact with the other gas. Difference between Electro-ethereal and Ethereo-ponderable Po
larization. 61. There are two species of electro-polarity which come under the head of statical electricity. One of these Faraday illustrates by supposing three bodies, A, B and C, in proximity, but not in contact, when A, being electrified, electrifies B, and B electrifies C by induction. This Faraday calls an action of the particles of the bodies concerned, whereas, by his own premises, it appears to me to be merely a superficial affection of the masses or of a circumambient ethereal matter. This species of polarization, to which the insulating power of air is necessary, affects the superficies of a body only, being displayed as well by a gilt
globe of glass, as a solid globe of metal. No sensible change appears to be produced in the ponderable conducting superficies by this inductive superficial electrification of masses; and of course no magnetism.
62. When a small image, of which the scalp has been abundantly furnished with long hair, is electrified, the hairy filaments extend themselves and move apart, as if actuated by a repulsive power: also when iron filings are so managed as to obey the influence of the poles of a powerful magnet (51), they arrange themselves in a manner resembling that of the electrified hair. There is, moreover, this additional analogy, that there is an attraction between two portions of hair differently electrified, like that which arises between filings differently magnetized. Yet the properties of the electrified hair and magnetized filings are, in some respects, utterly dissimilar. A conducting communication between differently electrified portions of hair would entirely neutralize the respective electrical states ; so that all the electrical phenomena displayed by them would cease. Yet such a communication made between the poles, exciting the filings, by any non-magnetic conductor, does not in the slightest degree lessen their polar affections and consequent power of reciprocal influence. Upon the electrified hair, the proximity or the contact of a steel magnet has no more effect than would result under like circumstances from any other metallic mass similarly employed; but by the approximation, and still more, the contact, of such a magnet, the affection of the filings may be enhanced, lessened, or nullified, according to the mode of its employment. In the case of the hair, the affection is superficial, and the requisite charging power must be in proportion to the extent of surface. In the case of the magnetized ferruginous particles, it is the mass which is affected, and, cæteris paribus, the more metal, the greater the capacity for magnetic power. In the instance of the electrified hair, as in every other of frictional excitement, the electrical power resides in irnponderable ethereo-electric atmospheres which adhere superficially to the masses, being liable to be unequally distributed upon them in opposite states of polarity, consequent to a superficial polarization of the exciting or excited ponderable masses; but in the instance of bodies permanently magnetic, or those rendered transiently magnetic by galvanic influence, the ethereo-electric matter and the ponderable atoms are inferred to be in a state of combination, forming ethereo-ponderable atoms; so that both may become parties to the movements and affections of which the positive and negative waves consist.
63. Thus an explanation is afforded of the hitherto mysterious diversity of the powers of a gold leaf electroscope and galvanoscopes, although both are to a wonderful degree sensitive; the latter to the most feeble galvanic discharge, the former to the slightest statical excitement; yet neither is in the most minute degree affected by the polarization which affects the other.
64. The charge which may exist in a coated pane affords another exemplification of statical or electro-ethereal polarity. In this case, according to Faraday, the particles of glass are thrown into a state of electro-polarity, and are, in fact, partially affected as if they belonged to a conductor; so that insulators and conductors differ only in the possession in a high degree by the one, of a susceptibility of which the other is possessed to an extent barely perceptible. The facts seem to me only to show, that either an insulator or conductor may be both affected by the same polarizing force, the transmission of which the one facilitates, the other prevents. I am under the impression that it is only by the diruptive process that electricity passes through glass; of course involving a fracture. It gets through a pane or jar, not by aid of the vitreous particles, but in despite of their opposing coherence. The glass in such cases is not liable to be fused, deflagrated, or dissipated, as conductors are. It is forced out of the way of the electrical waves, being incapable of becoming a party to them. Discharges will take place through a vacuity, rather than through the thinnest leaf of mica. But if, as Faraday has alleged, from within a glass flask hermetically sealed, an electrical charge has been found to escape, after a long time, it proves only that glass is not a perfect insulator, not that perfect insulation and perfect conduction are different extremes of the same property. On the contrary, the one is founded upon a constituie tion competent to the propagation within it of the electro-polarizing waves, with miraculous facility, while the other is founded either on an absolute incapacity, or comparatively an infinitely small ability to be the medium of their conveyance. The one extremely retards, the other excessively expedites its passage through a space otherwise void.*
Competency of a Wire to convey a Galvanic Discharge is as its
sectional area, while statical discharges of frictional electricity preferring the surface are promoted by its extension. Yet in proportion as such discharges are heavy, the ability of a wire to convey them and its magnetic energy become more dependent on its sectional area and less upon extent of surface.
65. Reference has been made to two modes of electrical conduction, in one of which the efficacy is as the surface; in the other, as the area of a section of the conductor. Although glass be substantially a non-conductor, the power of the surface of glass when moistened, or gilt, to discharge statical electricity,
* By a void, I mean a Torricellian vacuum. The omnipresence of the electroether must render the existence of a perfect void impossible.