Owing to the very considerable changes which constructional reasons necessitated in the relative positions of the center of pressure, center of gravity, and line of thrust from those which theoretical considerations pointed to as being best, it was decided in January, 1900, to build a one-quarter-size model of the large aerodrome, if a suitable engine capable of furnishing something like one and a half horse-power could be procured without delay. It was hoped that it might be possible to construct this model immediately without seriously interfering with the progress of the work on the large machine, and that some tests in free flight could then be made with it, which would give very much more reliable data from which to determine the balancing of the large aerodrome than had been obtained from the tests of the steam-driven models Nos. 5 and 6. A factor of uncertainty would still remain, due to the difference in size between the large machine and the model, which could be determined only by actual trial of the large machine itself; but by making the model an exact duplicate, on a smaller scale of the large machine, very valuable results could be obtained. Tests of it in free flight would involve, even with the probable attendant breakages, a comparatively small expenditure of time and money. A search was immediately begun for an engine builder who would undertake to furnish a suitable engine for this model. The specifications called for an engine developing one and a half horse-power on the Prony brake for five minutes without diminution in power caused by over heating. While it was desired if possible to get an engine which would come within the given weight and develop the required power for a longer time than five minutes, it was foreseen that the construction of a multiple-cylinder engine of so small a power made it necessary to resort to the air-cooled type, and that such an engine would be doing exceedingly well to develop its maximum power continuously for as much as five minutes. The only engine builder who could be found willing to undertake the construction of such an engine was the one already engaged in the construction of the larger engine. As this builder was already twelve months behind in the delivery of the large engine, it was felt that it would be unwise to give it to him, both because the work on it might still further delay him in the completion of the large one, and also because he was still having troubles with the large one, which it was not certain he would ever be able to overcome. After further consideration of the matter, however, it seemed so important to have a model which was an exact duplicate of the large machine for the [p227] making of tests, which might prevent not only serious damage but possibly fatal accidents, that upon the assurance of the engine builder that the undertaking of the small engine would in no way interfere with the completion