This helix is presented or held near to the antenna, and the length of it shortened until oscillations of the greatest intensity are produced in the helix as indicated by the use of an indicator of fluorescent paper.
The Fleming closed circuit wave meter, called by him a cymometer, consists of a sliding tube condenser and a long helix of wire forming an inductance; these are connected together and to a copper bar in such a manner that by one movement of a handle the capacity of the tubular condenser is altered in the same proportion as the amount of the spiral inductance which is included in the circuit.
Scierophyllous Plants.These are plants with evergreen leathery ives, and typical of tropical, sub-tropical, and warm temperate gions; e.g., Quercus Suber, Ilex Aquifohium, Hedera Helix, Eucalyps Globulus, Rosmarinus officinalis.
A, of Helix; B, of Eolis; a, ova; b, developing spermatozoa; c, common efferent duct.
A, Helix pomatia.
In Helix hortensis the spermatheca is simple.
In other species of Helix a second duct (as large in Helix aspersa as the chief one) is given off from the spermathecal duct, and in the natural state is closely adherent to the wall of the uterus.
But in rare cases in Helix aspersa a second spermatheca is found at the end of this second duct.
The nervous system of Helix is not favourable as an example on account of the fusion of the ganglia to form an almost uniform ring of nervous matter around the oesophagus.
- Hermaphrodite Reproductive Apparatus of the Garden Snail (Helix horlensis).
Helix nemoralis, L., of which H.
The species of Helix are all herbivorous, like the Pulmonata generally; snails and slugs are well-known enemies to the gardener.
The eggs of Helix are laid separately in the earth, each contained in a calcified shell; those of Limax are also separate, but the shell is gelatinous.
Helix hibernates in a torpid condition for about four months, and during this period the aperture of the shell is closed by a calcareous membrane secreted by the foot.
Ichthulin (see above) may be placed in this group; " helico-proteid," found in the serous gland of Helix pomatia, the vineyard snail, also belongs here.
(c) Univalvia spira regulari (= Cochleae): Argonauta, Nautilus, Conus, Cypraea, Bulla, Voluta, Buccinum, Strombus, Murex, Trochus, Turbo, Helix, Nerita, Haliotis.
In the steady motion under no force of such a body in medium, the centre of gravity describes a helix, while the axis escribes a cone round the direction of motion of the centre of ravity, and the couple causing precession is due to the dislacement of the medium.
Proposition 30 describes the construction of a curve of double curvature called by Pappus the helix on a sphere; it is described by a point moving uniformly along the arc of a great circle, which itself turns about its diameter uniformly, the point describing a quadrant and the great circle a complete revolution in the same time.
Thus if a point of the body be displaced from A to B, whilst the point which was at B is displaced to C, and that which was at C to D, the four points A, B, C, D lie on a helix whose axis is the common perpendicular to the bisectors of the angles ABC, BCD.
Such a complex motion is called screw-like or helical motion; for each point in the body describes a helix or screw round the axis of rotation, fixed or instantaneous as the case may ~ be.
In wheelwork of this kind the contact of each pair of teeth commences at the foremost end of the helical front, and terminates at the aftermost end; and the helix is of such a pitch that the contact of one pair of teeth shall not terminate until that of the next pair has commenced.
If a helix be described round the screw, crossing each turn of the thread at right angles, the distance between two corresponding points on two successive turns of the same thread, measured along this normal helix, may be called the normai pitch; and when the screw hns more than one thread the normal pitch from thread to thread i lay be called the normal divided pitch.
The d stance from thread to thread, measured on a circle described about the axis of the screw, called the pitch-circle, may be called the circumferential pitch; for a screw of one thread it is one circumone circumference ference; for a screw of ii threads, Let r denote the radius of the pitch circle; n the number of threads; 0 the obliquity of the threads to the pitch, circle, and of the normal helix to the axis; F,) Ipitch, P~ ~- the axial -~
The Romans are credited with having purposely introduced the edible snail (Helix pomatia) into England, and the common garden snail and slugs (Helix aspersa, Limax agrestis and Anion hortensis) have been unwittingly established in New Zealand.
Each wing forms a mobile helix or screw.
They accurately described the construction of DNA as a double helix and showed how its structure made replication both possible and reliable.