Telescopic work, clusters, [210]; double stars, [212].
Temporary stars, [223].
Terminator, the boundary-line between light and darkness on the moon or a planet.
Tides, [146].
Transit, the passage of an object across some fixed line, as the meridian, or between the eye of an observer and an apparently larger object, as that of Mercury or Venus over the disk of the sun, and the satellites of Jupiter over its disk; of a star, [65].
Ultimate force, the, [249].
Uranus, elements of, [173]; moons of, retrograde, [174]; perturbed by Neptune, [176].
Variable stars, [220].
Venus, [139].
Vernier, a scale to measure very minute distances.