Zenith Distance. Arc of a vertical circle intercepted between an observed point and the zenith.
Zenith Parallel. Small circle of celestial sphere, parallel to horizon and passing through all points having the same zenith distance.
Zenithal Projection. Projection of surface of a sphere by lines from centre to a plane that is tangent at the zenith.
Zenith Sector. Astronomical telescope that is weighted and pivoted, and fitted with an attachment for determining the true vertical. Used for measuring zenith distances.
Zephyr. A warm, light westerly breeze.
Zero.That point, in a scale, that is supposed to have no value, and from which the values of other points are reckoned. On one side of zero the values will be positive and negative on the other side.
Zigzag. To make good a mean course by steering short courses on either side of it. Done in wartime to make submarine attack more difficult. May be done, in normal circumstances, when searching for an inconspicuous object.
Zigzag Clock. Clock fitted for use when zigzagging. Special mechanism is incorporated to ring a bell when a course has been , steered for a pre-arranged time.
Zigzag Sailing. Sailing on alternate tacks.
Zinc Protector. Slab of zinc attached to underwater body of a ship to prevent steel of hull becoming electro positive to copper or copper alloy fittings exposed to salt water. Galvanic action breaks down zinc slab, which is renewable.
Zodiac. Twelve signs, or constellations, through which Sun travels in his annual course along the Ecliptic.