light, and that when compared with simple engines their power should be computed on the same basis. It will, therefore, be seen that if we do not take into consideration the steam supply or the amount of fuel and water necessary, the simple steam engine is an exceedingly light motor. But, as before stated, great improvements have recently been made in oil engines. I have thought much on this subject, and am of the opinion that if one had an unlimited supply of money, a series of experiments could be very profitably conducted with a view of adapting the oil engine for use on flying machines. If we use a steam engine, it is necessary to have a boiler, and at best a boiler is rather a large and heavy object to drive through the air. If we use an oil engine, no boiler is necessary, and the amount of heat carried over in the cooling water will only be one-seventh part of what is carried over in the exhaust from a steam engine of the same power. Therefore, the condenser only need be one-seventh part the size, and consequently should be made lighter with the tubes placed at a greater distance apart, and thus reduce the amount of power necessary to drive the machine through the air. Moreover, the supply of water necessary will be greatly reduced, and a cheaper and heavier oil may be employed, which is not so liable to take fire in case of an accident. It is then only a question as to whether an oil engine can be made so light as to keep its weight within that of a steam motor; that is, an oil engine in order to be available for the purpose must be as light, including its water supply, as a complete steam motor, which includes not only the engine, but also the boiler, the feed pumps, the water supply, the burner, the gas generator, and six-sevenths of the condenser. It requires a very perfect steam engine and boiler, not using a vacuum, to develop a horse-power with a consumption of 1-1/2 lbs. of petroleum per hour; but there are many oil engines which develop a horse-power with rather less than 1 lb. of oil per hour. It will, therefore, be seen that, as far as fuel is concerned, the oil engine has a decided advantage over the more complicated steam motor. Moreover, with an oil engine, the cooling water is not under pressure, so that the waste of water would be much less than with a steam engine, where the pressure is so high as to cause a considerable amount of waste through joints and numerous stuffing-boxes. The great advances that have been made of late years in electrical science and engineering have led many to believe that almost any knotty scientific question may be solved by the employment of electrical engineering, and a great deal has been written and said in regard to navigating the air by flying machines driven by electric motors.