Before I commenced my experiments, I made enquiries of all the prominent electrical engineering establishments where there was any likelihood of obtaining light and efficient electric motors, and found that it was impossible to obtain one that would develop a horse-power for any considerable time that would weigh less than 150 lbs. Since that time, notwithstanding that a great deal has appeared in the public prints about the efficiency and lightness of electric motors, I am unable to learn of any concern that is ready to furnish a complete motor, including a primary battery, which would supply the necessary current for two hours at a time, at a weight of less than 150 lbs. per horse-power, and as far as I have been able to ascertain from what I have myself seen, I cannot learn that there are any motors in practical use which do not weigh, including their storage batteries, at least 300 lbs. per horse-power. The last electric motor which I examined was in a boat; it was driven by a primary battery which weighed over 1,000 lbs. to the horse-power. From this I am of the opinion that we cannot at present look to electricity with any hope of finding a motor which is suitable for the purpose of aerial navigation. ENGINES. There is no question but what birds, and for that matter all animals, when considered as thermo-dynamic machines, are very perfect motors; they develop the full theoretical amount of energy of the carbon consumed. This we are quite unable to do with any artificial machine, but birds, for the most part, have to content themselves with food which is not very rich in carbon. It is quite true that a bird may develop from ten to fifteen times as much power from the carbon consumed as can be developed by the best steam engine, but, as an off-set against this, a steam engine is able to consume petroleum, which has at least twenty times as many thermal units per pound as the ordinary food of birds. The movement of a bird’s wings, from long years of development, has without doubt attained a great degree of perfection. Birds are able to scull themselves through the air with very little loss of energy. To imitate by mechanical means, the exact and delicate motion of their wings would certainly be a very difficult task, and I do not believe that we should attempt it in constructing an artificial flying machine. In Nature it is necessary that an animal should be made all in one piece. It is, therefore, quite out of the question that any part or parts should revolve. For land animals there is no question but what legs are the most perfect system possible, but in terrestrial locomotion by machinery, not necessarily in one piece, wheels are found to be much more effective and efficient. The swiftest animal can only travel for a minute of time at half the speed of a locomotive, while the locomotive is able to maintain its much greater speed for many hours at a time. The largest land animals only weigh about 5 tons, while the largest