1869.] Drainage. 655 fore spoken of, will be the centres, from which turn semicircles. Likewise, turn quadrants at the base, and a three- quarter foil at the apex. Fig. 11. Is a Semicircular Arch show- ing the lines of the voussoirs AC C C, &c, Which are radii of the semicircle. B is the Keystone. Fig. 12. Poly foil Arch. Divide the line of span into eight equal parts. From the points A and B, describe the segments A C and B C. Divide these into four parts each ; and, from the points of division as centres, turn semi- circles. Fig. 13. The Ogee Arch. Divide the span A to B into three parts ; and, from the points E and F, as centres, draw the semicircles A G F and B G E. Now, re-divide the line of space into four parts ; and, taking three of them, erect perpendiculars, A D and B C, at either end ; and join the points D C. Bisect the angles A C D and BCD with the lines D H and C H ; and, from the cen- tres C and D, with the radii C H and D H, describe segments connecting the arcs A G and B G with them, thus form- ing the Ogee Arch. Fig. 14. Tudor Arch. Divide the span-line A B into three parts, A E, E F, and F B. On the part E F construct a square, which will give the four points or centres. Draw the diagonals D E G and CFG. From the centre E describe the arc A G. From F, as a centre, de- scribe B G. Now, taking C as a centre, and C H as a radius, continue the seg- ment to the apex ; then, taking D as a centre, and D H as a radius, describe the segment connecting the springing arc ; and the Tudor Arch is complete. DRAINAGE THE proper draining of streets, is a subject of great interest to the civil engineer who has charge of a city, and many are the instances of failure in this matter to be found in our country, young as it is When a village is first laid out, it is an easy and an economical work to form a system of main drainage con- formable to the circumstances of the location ; yet how seldom do we see forecast displayed in this line. Vil- lages spring up, grow, and become cities, great cities, and it is just at this latter point that the grand error be- comes painfully evident to an over- taxed community. The error is one so often repeated, notwithstanding, that the whole thing becomes almost mysterious. Is there no ambition in the founders or projectors of those euibryo cities to lead them on to the contemplation of future advance of valuation, and to suggest to them the good policy of securing the great lines of arterial draining, while yet the prices of land and materials, and the cost of labor are within the limits of positive economy. We know of one large city in the West, that this subject applies to most intimately, where the location is such, that even surface draining has a natural facility of action, and yet the ad- vantage has not been taken at first, and to-day the difficulties increase, while the city treasury pales before the giant ad- versary to be overcome. Surface drainage, for streets with a quick descent is excessively disagree- able in rainy weather. Baltimore and Cincinnati, under the influence of the dreary god Pluvius, give a full elucida- tion of our ideas on this subject. In the former city, stepping-stones are built into the pavement, and rising high above it, to enable passengers to cross without being subjected to wet feet. In Cincinnati the rush of descending rain-
