Helix

“ Let the growth of the system, that is to say, be continuous and uniform; it is then evident that we have the elementary conditions for the development of a simple cylindrical helix; and this “primary helix” or “genetic spiral” we can now trace, winding round and round the stem, through A, B, C, etc. But if we can trace such a helix through A, B, C, it follows from the symmetry of the system, that we have only to join A to some other leaf to trace another spiral helix, such, for instance, as A, C, E, etc. ”

“ It was learned in Exp. 154 that inside of a helix (Fig. 123) the lines of force pass from the S to the N pole; they then spread out through the air and pass back on all sides of the coil to its S pole, as in the case of permanent magnets. The air around and inside of a helix offers a great resistance to the lines of force, and tends to weaken the [166] magnetic field. When part of the circuit consists of an iron core, which is a splendid conductor of lines of force, the magnetic field is greatly increased in strength. ”

“ If such a coil is suspended so as to turn freely, it tends to turn until the field within it is parallel to the earth's magnetic field. Such a suspended helix may therefore be used as a compass. In order to strengthen the magnetic field of a helix or solenoid, the space within its turns is filled with iron, often in the form [Pg 281] of small soft-iron wires. This bundle of iron wire is called the core of the helix. The core becomes strongly magnetized by the field of the helix while the current is flowing and quickly loses its magnetic force when the current is stopped. ”

“ A friend of mine, many years ago, brought a number of Helix lapicida from the South of England, and established them on some rocks on the banks of the Wear: they are now one of our recognized local species. I have also turned out Clausilias from Africa and from Syria, and various species of Helix from the latter country, in suitable localities in the county of Durham. But the latter perished the first winter: they could protect themselves against heat better than cold. ”

“ Dwarfing of the shell seems frequently to be the result of an elevated locality, not perhaps so much as the direct consequence of purer air and less barometric pressure, as of changes in the character of the food supply and in the humidity of the air. Several species of Helix have a variety minor which is characteristic of an Alpine habitat. Helix arbustorum var. alpestris, which is scarcely two-thirds the size of the type, occurs on the Swiss Alps in the region of perpetual snow. Sometimes a very slight elevation is sufficient to produce the dwarfed form. ”

“ The fresh-water snails which are not Pulmonates are the Paludinidae, Valvatidae and Ampullaridae, together with Neritina, a genus of the Neritidae. These all possess a fully developed gill-plume and are typical Pectinibranchs of the sub-order Taenioglossa, most of the members of which are marine.
The family Helicidae has a world-wide distribution. In Helix the spire forms a more or less obtuse-angled cone; there are above 1200 species, of which 24 are British. Helix nemoralis, L., of which H. hortensis is a variety, is one of the commonest forms. ”

“ It only occurs in well-grown specimens. When once it begins to form, it grows very rapidly, perhaps not more than a week being required for its entire formation.
Fig. 54.—Darts of British land snails: A, Hyalinia excavata Bean; B, Helix hortensis Müll.; C, Helix aspersa Müll. (After Ashford.)
The dart is almost confined to Helicidae, a certain number of exceptions being known which border on Helix. Hyalinia nitida and excavata are the only British species, not Helices, which are known to possess it. It has not been noticed to occur in the slugs, except in the N. American genus Tebennophorus. ”

“ The stem which we have begun to speak of as a cylinder is not strictly so, inasmuch as it tapers off towards its summit. The curve which winds evenly around this stem is, accordingly, not a true helix, for that term is confined to the curve which winds evenly around the cylinder: it is a curve in space which (like the spiral curve we have studied in our turbinate shells) partakes of the characters of a helix and of a logarithmic spiral, and which is in fact a logarithmic spiral with its pole drawn out of its original plane by a force acting in the direction of the axis. ”

“ FIG. 88.—Hot-wire ammeter.
Helix and tuning coils are divided into the "inductive" or "loose" and the "direct" or close coupled types. Inductive tuning coils are known as "loose-couplers" and "receiving transformers." Inductive helixes consist simply of two helixes, separated from one another as shown in the accompanying illustration. The upper helix, called the secondary, can be raised or lowered upon a central support. Varying the distance between the primary and secondary is varying the "coupling." ”

“ Helicidae and Naninidae are equally deficient, the former, indeed, attaining some numerical predominance in the extreme south, but the species are nearly all insignificant in size and colouring. It is only in Madagascar that Helix asserts itself. Arion, Limax, Hyalinia, Clausilia, and a [329] number of other genera abundant along the Mediterranean, are either altogether absent, or are very scantily represented. Land operculates, so characteristic of other tropical countries, are almost entirely wanting. ”

“ The form of this expression shews that the magnetic action of the currents in the disk is equivalent to that of a trail of images of the magnetic system in the form of a helix.
If the magnetic system consists of a single magnetic pole of strength unity, the helix will lie on the cylinder whose axis is that of the disk, and which passes through the magnetic pole. The helix will begin at the position of the optical image of the pole in the disk. The distance, parallel to the axis between consecutive coils of the helix, will be . ”

“ CELL SUB-DIVISION There is in nature another representation of hyper-dimensionality which, though difficult to demonstrate, is too interesting and significant to be omitted here.
Imagine a helix, intersected, in its vertical dimension, by a moving plane. If necessary to assist the mind, suspend a spiral spring above a pail of water, then raise the pail until the coils, one after another, become immersed. The spring would represent the helix, and the surface of the water the moving plane. ”

“ Thus Streptaxis, Helicarion, Macrochlamys, Kaliella, Sitala, Ariophanta, Rhysota, Hemiplecta, Diplommatina, Opisthoporus, Pterocyclus, Lagochilus, and Alycaeus all occur, especially in Southern China. The two points in which the sub-region bears special marks of individuality are Helix and Clausilia. The sub-genera of Helix which have their metropolis in China are Satsuma, Cathaica, Aegista, Acusta, Euhadra, Plectotropis, and Plectopylis. Sinistral forms (compare Fig. 213) are rather prevalent. ”

“ Powers of Vision in Land Mollusca.—The Helicidae are undoubtedly very short-sighted. Seldom emerging from their retreats except in twilight and darkness, they are naturally myopic, and see better in a subdued than in a bright light. Experiment has shown that a Helix can perceive an object better at 6 centimetres distance in a weak light than at 4 or 5 millimetres in a strong one. Cyclostoma elegans and Paludina vivipara are comparatively long-sighted, perceiving objects at a distance of 20 to 30 centimetres. ”

“ By having the center of the helix made of iron, instead of air, wood, or other non-magnetic bodies, the strength of the magnet is greatly increased. This central core may be fixed permanently in the coil, or be removable. For our purposes fixed cores are just as good as movable ones, and the coils are easily wound upon them. ”

“ Hazay finds [88] that the duration of life in Hyalinia is 2 years, in Helix pomatia 6 to 8, in Helix candicans 2 to 3, in Paludina 8 to 10, in Limnaea and Planorbis 3 to 4.
[40]
Growth of the Shell.—Mr. E. J. Lowe, many years ago, conducted [89] some interesting experiments on the growth of snails. The facts arrived at were—
(1) The shells of Helicidae increase but little for a considerable period, never arriving at maturity before the animal has once become dormant.
(2) Shells do not grow whilst the animal itself remains dormant. ”

“ The magnetizing force of a given helix is that force which tends to drive magnetic lines of force through the magnetic circuit interlinked with the helix. It is called magnetomotive force and is analogous to electromotive force, that is, the force which tends to drive an electric current through a circuit. ”

“ In size and number of cusps the first few laterals resemble the central tooth; in the extreme marginals the cusps often become irregular or evanescent. As a rule, the teeth are set squarely in the rows, with the exception of the extreme marginals, which tend to slope away on either side. In some Helicidae there is a slight approximation to the Zonitidae in the elongation of the first marginals.
The above is the type of radula occurring in the great family Helicidae, which includes not only Helix proper, with several thousand species, but also Arion, Bulimus, Ariolimax, and other genera. ”

“ Helix nemoralis, H. virgata, H. caperata, and H. hispida bury [41] themselves to grow; H. rotundata burrows into decayed wood; Hyalinia radiatula appears to remain on decaying blades of grass; Pupa umbilicata, Clausilia rugosa, and Buliminus obscurus bury their heads only.
The observations of Mr. W. E. Collinge [90] do not at all agree with those of Mr. Lowe, with regard to the mode in which land Mollusca enlarge their shells. He bred and reared most of the commoner forms of Helix and also Clausilia rugosa, but never saw them bury any part of their shell when enlarging it. ”

“ Suppose a small helix with many well insulated turns, as in experiment Fig. 17, has one of its ends connected to one of the terminals of the induction coil, and the other to a metal plate, or, for the sake of simplicity, a sphere, insulated in space. When the coil is set to work, the potential of the sphere is alternated, and the small helix now behaves as though its free end were connected to the other terminal of the induction coil. If an iron rod be held within the small helix it is quickly brought to a high temperature, indicating the passage of a strong current through the helix. ”

“ ACAVUS. Montfort. Fam. Limacinea, Blainville; Colimacea, Lamarck. A division of the genus Helix, which may be considered synonymous with De Ferrusac's sub-genus Helicogena. De Montfort has given H. Hæmastoma, as an example. Fig. 267.
ACCESSARY VALVES, are the smaller or less important testaceous plates, found on the hinge or dorsal margins of the true valves of some shells. Example, the small plates on the hinge of Pholas, fig. 55, a. The Pholades were placed by Linnæus and Bruguière among multivalve shells. ”

“ And here might properly be added the experimental distinction between a helix and a magnet, which Faraday subsequently pointed out (‘Exper. Res.,’ Art. 3273) : ‘Whereas an unchangeable magnet can never raise up a piece of soft iron to a state more than equal to its own, as measured by the moving wire, a helix carrying a current can develop in an iron core magnetic lines of force of a hundred or more times as much power as that possessed by itself when measured by the same means.’”
An article on the reduction of Mr. ”

“ This also may be absent (0) , or if present the size from base to apex measures as in the tragus under 3 mm. (1) , between 3 and 5 mm. (2) , or 5 — 7 mm. (3) . ANTI-HELIX: It is bent into an angle slightly or not at all (0) , the angle does not reach the level of the helix (1) , the angle is a little within or a little beyond the level of the helix (2) , it is very prominent, distinctly beyond the level of the helix (3) . Its prominence is a human feature.
As regards the HAIR, in all cases where there were a number of observations one or two of the oldest men had grizzled or even grey hair. ”

“ In a sphericall it is onely a crooked line; But in a conicall or Cylindraceall it may bee a right line, as is the side of a Cone and Cylinder. Therefore in the conversion or turning about of a line making a periphery, there is considered onely the distance; yea two points, one in the center, the other in the toppe, which therefore Aristotle nameth Rotundi principia, the principles or beginnings of a round.
12. An Helix is a crooked line which is unequally distant from the middest of the space, howsoever inclosed. ”

“ The core is also made to move very freely within the cavity of the helix, and is partially supported by means of springs which push upward against ears attached to the core. A ring of metal just below the core surrounds the carbon holder, and rests upon a floor or support. One edge of the ring is over a lifting tongue, which is attached to the core, while the opposite edge is a short distance below the crown of an adjustable set-screw. ”

“ Eocene——. Principal genera: Oopelta (no shell) , Arion (shell absent or formed of calcareous granules) , [441] Ariolimax, Geomalacus, Anadenus (subg. Prophysaon) , Hemphillia, Cryptostracon, Binneya, Helix (see below) , Cochlostyla, Bulimus (subg. Borus, Orphnus, Dryptus, Strophochilus, Pachyotus, and possibly Caryodes, Leucotaenia, Liparus, Livinhacea, Pachnodus, Rachis, Atopocochlis, Cerastus, Clavator belong here, or with Buliminus) , Berendtia, Rhodea. Pilsbry proposes [408] to group Helix as follows:
A. Eggs or young very large at birth:
(1) Macroön, incl. ”

“ Helcion, 405; protective coloration, 69 Helcioniscus, 405 Hele, F. M., on Hyalinia, 33; on Stenogyra, 34 Helicarion, 309, 316, 325, 332, 440; radula, 232; habits, 45, 67 Helicidae, radula, 232, 234 Helicina, 305, 306, 316–327, 338–358, 410; origin, 21; exterminated by cold, 24 Helicophanta, 335, 336, 441, 441 Heligmus, 449 Helix, 441; toothed aperture, 63; protective coloration, 70; variation, 87; carbonic acid, 163; eye, 181, 183; food, 179; smell, 194; jaw, 211; distribution, 285; tenacity of life, 37; breeding, 129 Helix alternata, 340 ”