With regard also to the amount of ammunition a Zeppelin can carry, this depends, of course, on the lifting power of the airship and the way in which it is distributed. The later Zeppelins are said to be able to carry a load of about 15,000 pounds, which is available for the crew, fuel for the engines, ballast, provisions, and spare stores, a wireless installation, and armament or ammunition. With engines of 500 horse power, something like 360 pounds of fuel is used per hour to drive them at full speed. Thus for a journey of twenty hours the vessel would need at least 7200 pounds of fuel. The necessary crew would absorb 2000 pounds more, and probably another 1500 pounds would be taken up for ballast and stores. Allowing a weight of 250 pounds for the wireless equipment, there would remain about 4000 pounds for bombs, or something less than two tons of explosives, for use against a target 458 miles from the base. This amount of ammunition could be increased proportionately as the conditions were altered by using a nearer base, or by proceeding at a slower and therefore more economical speed, &c. It is noteworthy that although the German airships were expected to act as scouts in the North Sea they do not appear to have accomplished anything in this direction. Possibly this has been due to the fear of attack by our men-of-war or aircraft if the movements were made in daytime, when alone they would be useful for this purpose. What happened during the Christmas Day affair, when, as the official report said, "a novel combat" ensued between the most modern cruisers on the one hand and the enemy's aircraft and submarines on the other, would not tend to lessen this apprehension. On the other hand, the greater stability of the atmosphere at night makes navigation after dark easier, and I believe that it has been usual in all countries for airships to make their trial trips at night. [Illustration: Radius of Action of a Modern Zeppelin The above outline map, which we reproduce from "The Naval Annual," shows in the dotted circle the comparative radius of action of a modern Zeppelin at half-power--about 36 knots speed--with other types of air machines, assuming her to be based on Cologne. It is estimated that aircraft of this type, with a displacement of about 22 tons, could run for 60 hours at half-speed, and cover a distance equivalent to about 2160 sea miles. This would represent the double voyage, out and home, from Cologne well to the north of the British Isles, to Petrograd, to Athens, or to Lisbon. The inner circle shows the radius of action of a Parseval airship at half-power--about 30 knots--based on Farnborough, and the small inner circle represents the radius of action of a hydro-aeroplane based on the Medway.]