The dirigibles--the type of airship commonly referred to as Zeppelins--have the advantage over the heavier-than-air machines of being almost silent in their operations, while at the same time they can remain for a longer time suspended in air over a camp or battleground without being detected. The Zeppelin is the development of the old balloon, made, however, in a conical shape with a long basket or car attached. They are driven by propellers similar to those used with aeroplanes, but as the power generated by the engines is merely used to drive the machines and has nothing to do with maintaining their position in the air, the motors do not have to be so powerful. They are steered by rudders. Some of the largest Zeppelins which have been leading factors in night raids conducted by the Germans on London and English coast resorts are capable of maintaining a speed of 60 miles an hour. One of these immense Zeppelins was reported to have covered 1300 miles in less than forty hours, covering the German borders, and still keeping in touch with its base. The Zeppelins, because of their large size, can carry large quantities of bombs, wireless apparatus, signals and electric searchlights. They can rise to a height that places them fairly beyond the range of the aerial guns used for fighting the air forces of the army. MANY KINDS OF BOMBS. The bombs used are as diversified as the crafts on which they are carried. The French aviators at one time dropped long steel billets or arrows which had swedged heads and sharpened points. These missiles, dropped from the height of a thousand feet or more, attained a velocity and force which made them dangerous weapons of the minor sort. The bombs, in the main, however, consist of jacketed shells containing high explosives, some of which are constructed on what is called the delayed-action principle. Such bombs explode after penetrating the fort or object which they strike, instead of going off by contact. Germany is said to have developed some of these that were of such size and power as to penetrate an armored ship. As much as 50 pounds of explosives or chemicals is declared to have been carried in some of the larger ones. The big dirigibles mount machine guns of superior range. Some of them have been armored to an extent, and to make them less easily detected they have been painted tints and colors to harmonize with the clouds and sky. Special kinds of gas have been used to fill the envelopes or bags, and instead of one large bag they consist of a series of bags enclosed in an envelope or casing, so that if a bullet would penetrate the envelope it would only destroy one of the gas bags, and not cause the whole thing to collapse.