always be introduced below the head to give the alignment the desired direction.[22] The small circles shown on the plan are “bumping posts.” On the left is shown a portion of the small raised bank at the edge of the road. [22] The curve can be quite sharp (see CHAP. I., Art. 2), and can be made, if necessary, within the length of the pitching. [Illustration: FIG. 16.] Figure 16 is a double regulator with needles. The scale is 30 feet to an inch. The spans are 15 feet. The roadway is on arches, but the regulating platform on steel beams. The needles are seen at the upstream sides of the regulators. They are worked from the platforms to which access is obtained through the gaps in the upstream parapets. The regulating platform should generally be only just clear of the F.S. level, and therefore lower than the roadway. [Illustration: NEEDLE REGULATOR AND BRIDGE. Needles lying on Bank. _To face p. 85._] Frequently the roadway of a bridge or small regulator is carried, not on arches, but on steel beams. The railings may be of wood or of gas pipe with the ends plugged, running through angle iron posts. In the case of such a regulator the roadway is sometimes so light that camels are not allowed to cross over. This causes unnecessary hardship. Bridges are not too numerous. If the regulation is done by gates, both road and platform are carried on arches. The regulators on inundation canals, and some on perennial canals, are not strong enough to admit of the flow of water being entirely stopped, so that the depth of water would be perhaps 10 feet upstream and nil downstream. This might cause the overturning of the piers, or the formation of streams under the floor. In such cases a maximum permissible heading up is decided on. Such orders are, in India, liable to be lost sight of in course of time, and they are, at least on inundation canals, where sudden emergencies often occur, hardly reasonable. An engine driver is not told that he must never entirely close his throttle valve. Regulators should be so designed that the water can be completely shut off. The following remarks show the chief points in favour of needles and horizontal planks respectively. _Advantages of Needles._ Needles can be placed or removed by one man. Needles do not require hooks, etc., which are liable to be broken or lost. A needle regulator requires few piers, and is therefore cheap. Water falling over planks throws a strain on the floor. Regulation with needles is easy and rapid. A jammed plank, especially if low down and not horizontal, may give great trouble. _Advantages of Planks._ Floating rubbish is not liable to collect above the Regulator because the water flows over the planks. By means of double grooves and earth filling, leakage can be quite stopped.