The light is generally carried at the top of a lattice-work steel tower. A support of this character can be taken to pieces, packed within small compass, and transported without difficulty, while erection is simplified and facilitated. Seeing that a large number of these beacons have been erected on headlands along the wildest stretches of the African continent and the loneliest coasts of Australia, where the methods of transport are restricted to coolies or mules, this method of packing is distinctly advantageous. The lamp is secured to the top of the tower, with the float cylinder of the lamp depending from the centre. In this arrangement, as a rule, a small tank is provided into which a drain-pipe empties the oil dropping from the drip-valve. In this way the oil may be drawn off, filtered, and used again in the float cylinder. In some instances the lamp is mounted upon a cast-iron column, in which case the float cylinder and the oil-drip tank are placed within the tube, access thereto being obtained through a door. The length of service on one charge varies according to the situation of the light. If in a very exposed and inaccessible place, it may be required to burn for two or three months without attention. Taken on the average, however, a monthly charge has been found to offer the greatest advantages. But in some places the longer interval is unavoidable. For instance, the Wigham light which is mounted upon the extremity of the Manora breakwater at Karachi cannot be approached for three months at a time during the monsoon. Under these circumstances a one-hundred-day service is imperative. The lenses are of the dioptric order, consisting of six elements built up into a strong gun-metal framework. The internal diameter naturally varies with the size and number of the wicks, and ranges from 10 inches for a 1-1/8 inch single wick, to 15 inches in the case of a 1-5/8 inch three-wick lamp. In the larger sizes a curved plate-glass pane is fitted outside the lens as a protection from the action of the weather. These storm-panes are set in copper doors, so that the glasses may be easily cleaned and polished when the lamp is being retrimmed. [Illustration: WILLSON GAS AND WHISTLING FLOATING LIGHT OFF EGG ISLAND, NOVA SCOTIA.] [Illustration: THE WILLSON “OUTER AUTOMATIC,” HALIFAX, NOVA SCOTIA.]