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The Helix ianthina, which is included by certain writers among the molluscs employed for dyeing purposes by the Phoenicians, is a shell of a completely different character, smooth and delicate, much resembling that of an ordinary land snail, and small compared to the others.
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. How does the insulated sphere act in this case? It can be a condenser, storing and returning the energy supplied to it, or it can be a mere sink of energy, and the conditions of the experiment determine whether it is more one or the other.
He placed a bar of iron in a coil of wire, and lifting the bar into the direction of the dipping needle, he excited by this action a current in the coil. On reversing the bar, a current in the opposite direction rushed through the wire. The same effect was produced when, on holding the helix in the line of dip, a bar of iron was thrust into it.
Opposite the two slits, a and a', there are two powerful converging lenses, l and l', whose foci coincide with two sorts of selenium plate rheostat, z and z'. The result of this arrangement is that as soon as one of the slits, as a consequence of the displacement of the helix, r, allows a luminous fascicle to escape, this latter falls upon the corresponding lens, which concentrates it and sends it to the selenium plates just mentioned.
The petiole of the leaf and the lower parts of the tendril, halfway between the upper leaflet and the lowest branch, are not sensitive. A tendril after curling from a touch became straight again in about 6 hrs., and was ready to re-act; but one that had been so roughly rubbed as to have coiled into a helix did not become perfectly straight until after 13 hrs.
These fins, or arms, are in reality wings, but wings disposed as a helix instead of as a paddle wheel. The helix advances in the direction of its axis. Is the axis vertical? Then it moves vertically. Is the axis horizontal? Then it moves horizontally.
Although Depuch Island had been visited before, there still remained something quite new to reward the diligent search that was made after objects of natural history: namely, a small kind of kangaroo, a land bird, and a shell, a species of Helix. The bird was shot by Mr.
A heavy shower of rain, by bringing out the landshells, enabled me to pick up half-a-dozen species of Helix, Bulimus, and Pupa, at the foot of the hedgerows; I was anxious to procure some to ascertain whether any were non-European forms; one was even quite a new species.
Melania turritissima, Forbes. a. Fragment of carapace of Trionyx. b. c. Bulimus ellipticus, Sowerby. Helix occlusa, Edwards. Paludina orbicularis. Planorbis discus, Edwards. Lymnea longiscata, Brand. Chara tuberculata, seed-vessel. d.
A short search among the damp stones and moss brought to light some small but interesting landshells, consisting of a pupiform Cyclostoma, a Carocolla, and five species of Helix.
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