The diagram on the wall represents sections of an electric launch built by Messrs. Yarrow and Company, and fitted up by the Electrical Power Storage Company, for the recent Electrical Exhibition in Vienna. She has made a great number of successful voyages on the River Danube during the autumn. Her hull is of steel, 40 feet long and 6 feet beam, and there are seats to accommodate forty adults comfortably. Her accumulators are stowed away under the floor, so is the motor, but owing to the lines of the boat the floor just above the motor is raised a few inches. This motor is a Siemens D2 machine, capable of working up to seven horse power with eighty accumulators. In speaking of the horse power of an electro motor, I always mean the actual power developed in the shaft, and not the electrical horse power; this, therefore, should not be compared to the indicated horse power of a steam engine. I am indebted to Messrs. Yarrow for the principal dimensions and other particulars of a high pressure launch engine and boiler, such as would be suitable for this boat. From these dimensions I prepared a second diagram representing the steam power, and when placed in position it will show at a glance how much space this apparatus will occupy. The total length lost in this way amounts to 12 feet, leaving for testing capacity only 15 feet, while that of the electric launch is 27 feet on each side of the boat; thus the accommodation is as fifteen to twenty-seven, or as twenty-two passengers to forty, in favor of the electric launch. Comparing the relative weights of the steam power and the electric power for this launch, we find that they are nearly equal--each approaches 50 cwt; but in the case of the steam launch we include 10 cwt. of coals, which can be stowed into the bunkers, and which allow fifteen hours continuous steaming, whereas the electric energy stored up will only give us seven and a half hours with perfect safety. I have here allowed 8 lb. of coal per indicated horse power per hour, and 10 horse power giving off 7 mechanical horse power on the screw shaft; this is an example of an average launch engine. There are launch engines in existence which do not consume one-half that amount of fuel, but these are so few, so rare, and so expensive, that I have neglected them in this account. Not many years ago, a steam launch carrying a seven hours supply of fuel was considered marvelous. Our present accumulaton supplies 33,000 foot pounds of work per pound of lead, but theoretically one pound of lead manifests an energy equal to 360,000 foot pounds in the separation from its oxide; and in the case of iron, Prof. Osborne Reynolds told us in this place, the energy evolved by its oxidation is equivalent to 1,900,000 foot pounds per pound of metal. How nearly these limits may be approached will he the problem of the chemist; to prophesy is dangerous, while science and its applications are advancing at this rapid rate.