Volume I Part 22 (1/2)

_Cold from each point cerulean l.u.s.tres gleam._

CANTO I. l. 339.

ELECTRIC POINTS.

There was an idle dispute whether k.n.o.bs or points were preferable on the top of conductors for the defence of houses. The design of these conductors is to permit the electric matter acc.u.mulated in the clouds to pa.s.s through them into the earth in a smaller continued stream as the cloud approaches, before it comes to what is termed striking distance; now as it is well known that acc.u.mulated electricity will pa.s.s to points at a much greater distance than it will to k.n.o.bs there can be no doubt of their preference; and it would seem that the finer the point and the less liable to become rusty the better, as it would take off the lightening while it was still at a greater distance, and by that means preserve a greater extent of building; the very extremity of the point should be of pure silver or gold, and might be branched into a kind of brush, since one small point can not be supposed to receive so great a quant.i.ty as a thicker bar might conduct into the earth.

If an insulated metallic ball is armed with a point, like a needle, projecting from one part of it, the electric fluid will be seen in the dark to pa.s.s off from this point, so long as the ball is kept supplied with electricity. The reason of this is not difficult to comprehend, every part of the electric atmosphere which surrounds the insulated ball is attracted to that ball by a large surface of it, whereas the electric atmosphere which is near the extremity of the needle is attracted to it by only a single point, in consequence the particles of electric matter near the surface of the ball approach towards it and push off by their greater gravitation the particles of electric matter over the point of the needle in a continued stream.

Something like this happens in respect to the diffusion of oil on water from a pointed cork, an experiment which was many years ago shewn me by Dr. Franklin; he cut a piece of cork about the size of a letter-wafer and left on one edge of it a point about a sixth of an inch in length projecting as a tangent to the circ.u.mference. This was dipped in oil and thrown on a pond of water and continued to revolve as the oil left the point for a great many minutes. The oil descends from the floating cork upon the water being diffused upon it without friction and perhaps without contact; but its going off at the point so forcibly as to make the cork revolve in a contrary direction seems a.n.a.logous to the departure of the electric fluid from points.

Can any thing similar to either of these happen in respect to the earth's atmosphere and give occasion to the breezes on the tops of mountains, which may be considered as points on the earths circ.u.mference?

FAIRY-RINGS.

There is a phenomenon supposed to be electric which is yet unaccounted for, I mean the Fairy-rings, as they are called, so often seen on the gra.s.s. The numerous flashes of lightning which occur every summer are, I believe, generally discharged on the earth, and but seldom (if ever) from one cloud to another. Moist trees are the most frequent conductors of these flashes of lightning, and I am informed by purchasers of wood that innumerable trees are thus cracked and injured. At other times larger parts or prominences of clouds gradually sinking as they move along, are discharged on the moisture parts of gra.s.sy plains. Now this k.n.o.b or corner of a cloud in being attracted by the earth will become nearly cylindrical, as loose wool would do when drawn out into a thread, and will strike the earth with a stream of electricity perhaps two or ten yards in diameter. Now as a stream of electricity displaces the air it pa.s.ses through, it is plain no part of the gra.s.s can be burnt by it, but just the external ring of this cylinder where the gra.s.s can have access to the air, since without air nothing can be calcined. This earth after having been so calcined becomes a richer soil, and either funguses or a bluer gra.s.s for many years mark the place. That lightning displaces the air in its pa.s.sage is evinced by the loud crack that succeeds it, which is owing to the sides of the aerial vacuum clapping together when the lightning is withdrawn. That nothing will calcine without air is now well understood from the acids produced in the burning of phlogistic substances, and may be agreeably seen by suspending a paper on an iron p.r.o.ng and putting it into the centre of the blaze of an iron-furnace; it may be held there some seconds and may be again withdrawn without its being burnt, if it be pa.s.sed quickly into the flame and out again through the external part of it which is in contact with the air. I know some circles of many yards diameter of this kind near Foremark in Derbys.h.i.+re which annually produce large white funguses and stronger gra.s.s, and have done so, I am informed, above thirty years. This increased fertility of the ground by calcination or charring, and its continuing to operate so many years is well worth the attention of the farmer, and shews the use of paring and burning new turf in agriculture, which produces its effect not so much by the ashes of the vegetable fibres as by charring the soil which adheres to them.

These situations, whether from eminence or from moisture, which were proper once to attract and discharge a thunder-cloud, are more liable again to experience the same. Hence many fairy-rings are often seen near each other either without intersecting each other, as I saw this summer in a garden in Nottinghams.h.i.+re, or intersecting each other as described on Arthur's seat near Edinburgh in the Edinb. Trans. Vol. II. p. 3.

NOTE XIV.--BUDS AND BULBS.

_Where dwell my vegetative realms benumb'd In buds imprison'd, or in bulbs intomb'd._

CANTO I. l. 459.

A tree is properly speaking a family or swarm of buds, each bud being an individual plant, for if one of these buds be torn or cut out and planted in the earth with a gla.s.s cup inverted over it to prevent its exhalation from being at first greater than its power of absorption, it will produce a tree similar to its parent; each bud has a leaf, which is its lungs, appropriated to it, and the bark of the tree is a congeries of the roots of these individual buds, whence old hollow trees are often seen to have some branches flourish with vigour after the internal wood is almost intirely decayed and vanished. According to this idea Linneus has observed that trees and shrubs are roots above ground, for if a tree be inverted leaves will grow from the root-part and roots from the trunk-part. Phil. Bot p. 39. Hence it appears that vegetables have two methods of propagating themselves, the oviparous as by seeds, and the viviparous as by their buds and bulbs, and that the individual plants, whether from seeds or buds or bulbs, are all annual productions like many kinds of insects as the silk-worm, the parent peris.h.i.+ng in the autumn after having produced an embryon, which lies in a torpid state during the winter, and is matured in the succeeding summer. Hence Linneus names buds and bulbs the winter-cradles of the plant or hybernacula, and might have given the same term to seeds. In warm climates few plants produce buds, as the vegetable life can be compleated in one summer, and hence the hybernacle is not wanted; in cold climates also some plants do not produce buds, as philadelphus, frangula, viburnum, ivy, heath, wood-nightshade, rue, geranium.

The bulbs of plants are another kind of winter-cradle, or hybernacle, adhering to the descending trunk, and are found in the perennial herbaceous plants which are too tender to bear the cold of the winter.

The production of these subterraneous winter lodges, is not yet perhaps clearly understood, they have been distributed by Linneus according to their forms into scaly, solid, coated, and jointed bulbs, which however does not elucidate their manner of production. As the buds of trees may be truly esteemed individual annual plants, their roots const.i.tuting the bark of the tree, it follows that these roots (viz. of each individual bud) spread themselves over the last years bark, making a new bark over the old one, and thence descending cover with a new bark the old roots also in the same manner. A similar circ.u.mstance I suppose to happen in some herbaceous plants, that is, a new bark is annually produced over the old root, and thus for some years at least the old root or caudex increases in size and puts up new stems. As these roots increase in size the central part I suppose changes like the internal wood of a tree and does not possess any vegetable life, and therefore gives out no fibres or rootlets, and hence appears bitten off, as in valerian, plantain, and devil's-bit. And this decay of the central part of the root I suppose has given occasion to the belief of the root-fibres drawing down the bulb so much insisted on by Mr. Milne in his Botanical Dictionary, Art.

Bulb.

From the observations and drawings of various kinds of bulbous roots at different times of their growth, sent me by a young lady of nice observation, it appears probable that all bulbous roots properly so called perish annually in this climate: Bradley, Miller, and the Author of Spectacle de la Nature, observe that the tulip annually renews its bulb, for the stalk of the old flower is found under the old dry coat but on the outside of the new bulb. This large new bulb is the flowering bulb, but besides this there are other small new bulbs produced between the coats of this large one but from the same caudex, (or circle from which the root-fibres spring;) these small bulbs are leaf-bearing bulbs, and renew themselves annually with increasing size till they bear flowers.

Miss ---- favoured me with the following curious experiment: She took a small tulip-root out of the earth when the green leaves were sufficiently high to show the flower, and placed it in a gla.s.s of water; the leaves and flower soon withered and the bulb became wrinkled and soft, but put out one small side bulb and three bulbs beneath descending an inch into the water by long processes from the caudex, the old bulb in some weeks intirely decayed; on dissecting this monster, the middle descending bulb was found by its process to adhere to the caudex and to the old flower-stem, and the side ones were separated from the flower- stem by a few shrivelled coats but adhered to the caudex. Whence she concludes that these last were off-sets or leaf-bulbs which should have been seen between the coats of the new flower-bulb if it had been left to grow in the earth, and that the middle one would have been the new flower-bulb. In some years (perhaps in wet seasons) the florists are said to lose many of their tulip-roots by a similar process, the new leaf-bulbs being produced beneath the old ones by an elongation of the caudex without any new flower-bulbs.

By repeated dissections she observes that the leaf-bulbs or off-sets of tulip, crocus, gladiolus, fritillary, are renewed in the same manner as the flowering-bulbs, contrary to the opinion of many writers; this new leaf-bulb is formed on the inside of the coats from whence the leaves grow, and is more or less advanced in size as the outer coats and leaves are more or less shrivelled. In examining tulip, iris, hyacinth, hare- bell, the new bulb was invariably found _between_ the flower-stem and the base of the innermost leaf of those roots which had flowered, and _inclosed_ by the base of the innermost leaf in those roots which had not flowered, in both cases adhering to the caudex or fleshy circle from which the root-fibres spring.

Hence it is probable that the bulbs of hyacinths are renewed annually, but that this is performed from the caudex within the old bulb, the outer coat of which does not so shrivel as in crocus and fritillary and hence this change is not so apparent. But I believe as soon as the flower is advanced the new bulbs may be seen on dissection, nor does the annual increase of the size of the root of cyclamen and of aletris capensis militate against this annual renewal of them, since the leaf- bulbs or off-sets, as described above, are increased in size as they are annually renewed. See note on orchis, and on anthoxanthum, in Vol. II.

of this work.

NOTE XV.--SOLAR VOLCANOS.

_From the deep craters of his realms of fire The whirling sun this ponderous planet hurld_.