What about the power plants of the future aircraft? Will the internal-combustion engine continue to reign supreme, or will increasing power demands of the huge planes to come lead to the development of suitable steam-engines? Will the use of petroleum continue to be one of the triumphs of aviation, or will the time come when substitutes may be successfully utilized?
For aerial motive-power, the principal requirements are: great power for weight with a fairly high factor of safety, compactness, reliability of operation under flying conditions, and safety from fire. Bulk and weight of steam-driven equipment apparently impose severe restrictions upon its practical development for present aircraft purposes, but who is willing to classify its future use as an absurdity?
Steam operation in small model airplanes is no innovation. Langley, in 1891-1895, built four model airplanes, one driven by carbonic-acid gas and three by steam-engines. One of the steam-driven models weighed thirty pounds, and on one occasion flew a distance of about three thousand feet. In 1913 an Englishman constructed a power plant weighing about two pounds which consisted of a flash boiler and single-acting engine. This unit employed benzolin, impure benzine, as fuel, and propelled a model plane weighing five pounds.
Power Plant Engineering, Chicago, June 1, 1919
Making a Brief. The next step after making outlines or briefs of material already organized is to make your own from material you gather. Speeches you have already prepared or considered as fit for presentation will supply you with ideas if you cannot work up new material in a short time. At first you will be more concerned with the form than the meaning of the entries, but even from the first you should consider the facts or opinions for which each topic or statement stands. Weigh its importance in the general scheme of details. Consider carefully its suitability for the audience who may be supposed to hear the finished speech. Discard the inappropriate. Replace the weak. Improve the indefinite. Be sure your examples and illustrations are apt.
Be wary about statistics. In listening to an address many people begin to distrust as soon as figures are mentioned. Statistics will illustrate and prove assertions, but they must be used judiciously. Do not use too many statistics. Never be too detailed. In a speech, $4,000,000 sounds more impressive than $4,232,196.96. Use round numbers. Never let them stand alone. Show their relationship. Burke quotes exact amounts to show the growth of the commerce of Pennsylvania, but he adds that it had increased fifty fold. A hearer will forget the numbers; he will remember the fact.
Similar reasons will warn you concerning the use of too many dates. They can be easily avoided by showing lapses of time—by saying, "fifty years later," or "when he was forty-six years old," or "this condition was endured only a score of months."
The chapters on introductions, conclusions, and planning material will have suggested certain orders for your briefs. Glance back at them for hints before you attempt to make the general scheme. Let two factors determine your resultant development—the nature of the material itself and the effect you want to produce.
In argumentative speeches a usual, as well as excellent, order is this: