TROPICS

, in Astronomy, two fixed circles of the sphere, drawn parallel to the equator, through the solstitial points, or at such distance from the equator, as is equal to the sun's greatest recess or declination, or to the obliquity of the ecliptic.

Of the two Tropics, that on the north side of the equator, passes through the first point of Cancer, and is therefore called the Tropic of Cancer. And the other on the south side, passing through the first point of Capricorn, is called the Tropic of Capricorn.

To determine the distance between the two Tropics, and thence the sun's greatest declination, or the obliquity of the ecliptic; observe the sun's meridian altitude, both in the summer and winter solstice, and subtract the latter from the former, so shall the remainder be the distance between the two Tropics; and the half of this will be the quantity of the greatest declination, or the obliquity of the ecliptic; the medium of which is now 23° 28′ nearly.

, in Geography, are two lesser circles of the globe, drawn parallel to the equator through the beginnings of Cancer and Capricorn, being in the planes of the celestial Tropics, and consequently at 23° 28′ distance either way from the equator.

TROY-Weight, anciently called Trone weight, is supposed to be taken from a weight of the same name in France, and that from the name of the town of Troyes there.

The original of all weights used in England, was a corn or grain of wheat gathered out of the middle of the ear, and, when well dried, 32 of them were to make one pennyweight, 20 pennyweights 1 ounce, and 12 ounces 1 pound Troy. Vide Statutes of 51 Hen. III; 31 Ed. I. and 12 Hen. VII.

But afterward it was thought sufficient to divide the said pennyweight into 24 equal parts, called grains, being the least weight now in common use; so that the divisions of Troy weight now are these:

By Troy-weight are weighed jewels, gold, silver, and all liquors.