44 4 EXPLANATION QF THE PRINCIPAL TERMS '

Horizon, (Rational,) a great circle which is parallel tothe former, and whose two poles are the zenith andnadir.

Horizontal, something relating to the Horizon, orthat which is taken in, or on a level with the Horizon.

Hour Circles, the same vyith meridians, or greatcircles which pass through the poles of the world, andare perpendicular to the equator.

Hour, the 24th part of a natural day, which Astronomersalways begin to reckon from noon.

Hydra, a southern constellation composed of fifty-threestars.

Hypothesis, a supposition, a system formed upon someprinciple which has not been proved,

I.

Immersion, the moment when an eclipse begins, orwhen a planet enters into the dark shadow.

Inclination, the angle which the orbit of one planetmakes with that of another.

Indefinite, or Indeterminate, that to which the humanmind cannot six any certain bounds or limits.

Indus, a southern constellation composed of twelve stars,

Inferior Planets, are those that move at a less distancefrom the fun than the earth ; which are Mercury andVenus, *

Ingress, is the fun's entrance into any sign or other partof the ecliptic.

Intercalary Pay, the odd day, which is made up ofthe six hours every fourth or leap-year.

Julian Year, thp account of time instituted by JuliusCæsar, which is now called the old stile.

JURifER, the largest planet in pur system, and the sifchin order from the fun.

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