TO DETERMINE THE CURVE, LIMITING THE EXTREMEPOINTS OF RANGE OF BODIES, PROJECTED WITH AGIVEN HORIZONTAL VELOCITY IN A HORIZONTAL DI-RECTION AT HEIGHTS, EACH EQUAL TO THE HORI-ZONTAL VELOCITY, ABOVE ANY POINT OF A CURVE •OR THE EXTRADOS TO A GIVEN INTRADOS OF AN ARCHAND OF ITS ABUTMENT WALL, ASSUMING THE HEIGHTOF THE KEY-STONE EQUAL TO THE HORIZONTAL VE-LOCITY.

GENERAL CONSTRUCTION.

13. Let A be the vertex of the intrados of an arch,J ‘ and V the vertex of the extrados. Through anypoint E in the intrados draw FH at right angles tothe tangent at F. Draw the vertical line FG equalto AV, and the horizontal line GI, cutting FH in H.Make HI equal to GH. From HI let fall the tri-angle HIK, similar to the triangle FGH, FG andHI, homologous sides. K is a point in the ex-trados.

beaucoup pres, aux piles la meme epaisseur qu’aux culees.”Page 625- he says, “ On a cru devoir leur donner au moins pourepaisseur le double de cette longueur de coupe,” speaking of thesection of the key or height of it. — Gauthey, vol. 1. page 348.says, of bearing piers, “ Quand leur objet est seulement de porterles poids des arches, la resistance de la pierre dont elles sont con-struites est la principale consideration a laquelle on doive avoiregard, et laseule qu’on puisse soumettre au ealcul.” See the for-mula; to determine the height of the key of an arch, page 43.