Celestial Meridian. Great circle of celestial sphere that is a secondary circle to Equinoctial. Declination is measured on it.
Celestial Poles. Those points in celestial concave that are in the zenith at north and south poles of Earth.
Celestial Sphere. General name for the heavens, or sky. Heavenly bodies are assumed to be on the interior surface of a hollow sphere. Name is sometimes given to a globe showing places of stars on its outer surface. It is preferable to call this a 'star globe'.
Cellular System.Ship construction in which double bottom is divided into small spaces by erection of intercostal longitudinals between floors.
Celox. Fast, single-banked vessel of Rhodes in classic times.
Celonavigation. Name suggested by Harbord (Glossary of Navigation) to denote navigational workings requiring observations of celestial bodies. Astro-navigation.
Celsius. (Centigrade) Graduation of thermometer scale in which the freezing temperature is 0°C and boiling point 100°C.
Cement. Calcined chalk and clay in powder form. Mixed with water and an aggregate (sand, etc.). Is alkaline, so neutralising acids. Used in ships as protection against abrasion, corrosion, percussion, to give additional strength and for stopping leaks.