When the ford is deeper than this, the cannoneers must carry over the cartridges, fuzes, and primers in the pouches, which they hold above the water. The chests are sometimes removed and taken over in boats. In crossing streams that cannot be forded, when there are no bridges, the horses are swum, and the carriages and harness crossed on rafts, etc. PASSAGE OF MILITARY BRIDGES. At the entrance of the bridge the lead-and swing-drivers dismount and lead their pairs. A distance of 12 yards is taken between the carriages, and the gait is free and decided; the drivers keep the carriages as near the middle of the floor as possible. If the flooring be wet, battens should be nailed across it to keep the horses from falling. If the bridge begins to rock, the passage of the column is suspended. In passing over a flying bridge all the drivers dismount and hold their horses; the lead-and swing-horses should be taken out and led onto the bridge or boat; the brakes should be applied to the rear, so that the carriage cannot be run back. PASSAGE ON ICE. Ice 3 or 4 inches thick will bear infantry. Ice 4½ inches thick will bear light guns or cavalry. Ice 6 inches thick will bear heavy field-guns. FACING A BATTERY TO THE REAR ON A NARROW ROAD. All the carriages are moved close to one side of the road, and the pieces and caissons unlimbered and brought about; the limbers then take their places in front of their carriages by an about, and the carriages are limbered up; if there be not room for the limbers to execute an about, the horses are taken out. If the road be so narrow that the limbers cannot pass the carriages, the trails of the pieces and the stocks of the caissons are carried around until perpendicular to the road, and are then placed against the bank, the wheels being run close to it; on an embankment, or a road with ditches on each side, the carriages are run as close to the edge as possible, the wheels chocked or locked, and the trails and stocks held up while the limbers pass. THE ODOMETER. The odometer registers the number of revolutions of the wheel to which it is attached. The distance measured by the odometer is not exact, owing to the slip of the wheel. =To Read the Odometer.=--Lift the reading-circle from its box and note the number on the inner wheel to the left of the zero; this will be the first two figures of the reading, and the number on the outer wheel to the left of the pointer will be the next two.