CROSS
, in Surveying, is an instrument consisting of a brass circle, divided into 4 equal parts, by two lines crossing each other in the centre. At each extremity of these lines is fixed a perpendicular sight, with small holes below each slit, for the better discovering of distant objects. The cross is mounted on a stasf, or stand, to fix it in the ground, and is very useful for measuring small pieces of land, and taking offsets, &c.
Ex. Suppose it be required to survey the field ABCDE with the Cross. Measure along the diagonal line AC, and observe, with the Cross, when you are perpendicularly opposite to the corners, as at F, G, H, and from thence measure the perpendiculars FE, GB, | HD. When you think you are nearly opposite a corner, set up the cross, with one of the bars or cross lines in the direction AC; then look through the sights of the other cross bar for the corner, as B; if it be seen through them, the cross is fixed in the right place; if not, take it up and move it backward or forward in the line AC, till the point B be seen through those sights; and then you have the true place of the perpendicular.
Invention of the Cross, Inventio Crucis, an ancient feast, which is still retained in our calendar, and solemnized on the 3d of May, in memory of the sinding of the true Cross of Christ, deep in the ground, on Mount Calvary, by St. Helena, the mother of Constantine; where she erected a church for the preservation of part of it: the rest being brought to Rome, and deposited in the church of the Holy Cross of Jerusalem.
Exaltation of the Cross, an ancient feast, held on the 14th of September, in memory of this, that Heraclitus restored to Mount Calvary the true cross, in 642, which had been carried off, 14 years before, by Cosroes king of Persia, upon his taking Jerusalem from the emperor Phocas. This feast is still retained in our calendar, on Sept. 14, under the denomination of Holy Rood, or Holy Cross.
Cross-Multiplication, a method used chiefly by artificers in multiplying feet and inches by feet and inches, or the like; so called, because the factors are multiplied cross-wise, thus:
| f. | i. | |
| 9 | 10 | |
| 6 | 8 | |
| 59 | 0 | |
| 6 | 6 | 8′ |
| 65 | 6 | 8 |
Cross-Staff, or Fore-Staff, is a mathematical instrument of box, or pear tree, consisting of a square staff, of about 3 feet long, having each of its faces divided like a line of tangents, and having 4 cross pieces of unequal lengths to fit on to the staff, the halves of these being as the radii to the tangent lines on the faces of the staff.—The instrument was used in taking the altitudes of the celestial bodies at sea.
