Having thus shortly outlined the development of the one, we will endeavor to discover the fundamental difference between aeroplane and airship. It is simply the matter of “lift” obtained in the case of the latter from the property of being lighter than air, whereas the other craft being heavier than air must obtain its “lift” by mechanical propulsion. The airship is merely an improvement on the old-fashioned balloon: a balloon to which mechanical propulsion has been applied. Different in shape, indeed, and fitted out with many modern improvements, its flight is still governed by the same laws of “aerostatics.” For practical purposes we will divide the airship into two portions: the envelope or balloon, and the car. Atmospheric conditions influence the envelope to no small degree. The effect of heat upon gas--with which the envelope is filled--is to make it expand, and consequently cause the craft to rise. Cold, on the other hand, causes the gas to contract, and the craft to descend. Air pressure is another factor which must be taken into account, and this is greatest at sea-level. The greater the altitude, the less the pressure becomes, and the less pressure on the outside surface of the envelope the easier it is for the gas to expand; but this is compensated for by the fact that the atmosphere is considerably cooler at a high altitude. There are three types of airship: the “non-rigid,” in which the two portions, the car and the envelope, are entirely separate portions, being held together by means of rigging; “semi-rigged,” in which the car is partly attached to the envelope, a type greatly favored by French and Italians; and the “rigid” airship, of which both car and envelope are in the same framework. The Zeppelin is of the latter class. Like other great airships the Zeppelin does not rely on one single balloon for “lift.” Instead, the envelope forms merely the outer covering for eighteen balloonettes, which can be regulated in the matter of expansion and contraction from the control-car of one of the three gondolas below. We have by no means yet seen these wonderful craft at their deadliest; the German pilots are extremely brave men, yet lack that initiative and dash peculiar to the British Air Service. Were the position reversed, one dreads to think what might happen to this country. The future is all with the airship, in the rôle of commerce-bearing aircraft. The aeroplane and all heavier-than-air craft are of little value save as units of war, and even then their uses are infinitesimal when compared with those of the Zeppelin. And the secret of the success of the Zeppelin is that she has the “lift,” double and treble the lift of the aeroplane, and is developing beyond belief, whereas, in proportion, the aeroplane develops little year by year.