NOCTILUCA
, a species of phosphorus, so called because it shines in the night, without any light being thrown on it: such is the phosphorus made of urine. By which it stands distinguished from some other species of phosphorus, which require to be exposed to the sunbeams before they will shine; as the Bononian-stone, &c. —Mr. Boyle has a particular Treatise on this subject.
NOCTURNAL Arch, is the arch of a circle described by the sun, or a star, in the night.
Nocturnal, or Nocturlabium, denotes an instrument, chiefly used at sea, to take the altitude or depression of the pole star, and some other stars about the pole, for finding the latitude, and the hour of the night.
There are several kinds of this instrument; some of which are projections of the sphere; such as the hemispheres, or planispheres, on the plane of the equinoctial. The seamen commonly use two kinds; the one adapted to the pole star and the first of the guards of the Little Bear; the other to the pole star and the pointers of the Great Bear.
The Nocturnal consists of two circular plates (fig. 15, pl. xiii) applied over each other. The greater, which has a handle to hold the instrument, is about 2 1/2 inches diameter, and is divided into 12 parts, answering to the 12 months; also each month subdivided into every 5th day; and in such manner, that the middle of the handle corresponds to that day of the year in which the star here respected has the same right ascension with the sun.
When the instrument is fitted for two stars, the han- dle is made moveable. The upper circle is divided into 24 equal parts, for the 24 hours of the day, and each hour subdivided into quarters, as in the figure. These 24 hours are noted by 24 teeth; to be told in the night. In the centre of the two circular plates is adjusted a long index A, moveable upon the upper plate. And the three pieces, viz, the two circles and index, are joined by a rivet which is pierced through the centre, with a hole 2 inches in diameter, for the star to be observed through.
To Use the Nocturnal. Turn the upper plate till the longest tooth, marked 12, be against the day of the month on the under plate; and bringing the instrument near the eye, suspend it by the handle, with the plane nearly parallel to the equinoctial; then viewing the pole-star through the hole in the centre, turn the index about till, by the edge coming from the centre, you see the bright star or guard of the Little Bear, if the instrument be fitted to that star: then that tooth of the upper circle, under the edge of the index, is at the hour of the night on the edge of the hour-circle: which may be known without a light, by counting the teeth from the longest, which is for the hour of 12.
NODATED Hyperbola, one, so called by Newton, which by turning round decussates or crosses itself: as in the 2d, and several other species, of his Enumeratio Linearum Tertii Ordinis.
