After seven minutes’ steaming, 2·25 lbs. of water were condensed in five minutes. It will be seen from these experiments that an atmospheric condenser, if properly constructed, is fairly efficient. Roughly speaking, it requires 2,400 times as much air in volume as of water to use as a cooling agent. With the steam engine condenser only a relatively small amount of water is admitted, and this is found to be sufficient; but in an atmospheric condenser working in the atmosphere, it must be as open as possible, so that no air which has struck one heated surface can ever come in contact with another. CHAPTER V. EXPERIMENTS WITH APPARATUS ATTACHED TO A ROTATING ARM. From what information I have at hand, it appears that Prof. Langley made his first experiments with a small apparatus, using aeroplanes only a few inches in dimensions which travelled round a circle perhaps 12 feet in diameter. With this little apparatus, he was able to show that the lifting effect of aeroplanes was a great deal more than had previously been supposed. After having made these first experiments, he seems to have come to the conclusion that Newton’s law was erroneous. Shortly after Langley had made these experiments on what he called a whirling table, which, however, was not a very appropriate name, I made an apparatus myself, but very much larger than that employed by Prof. Langley. I reckoned the size of my aeroplanes in feet, where he had reckoned his in inches. The circumference of the circle around which my aeroplanes were driven was exactly 200 feet, and shortly after this Langley constructed another apparatus, the same dimensions as my own. From an engraving which I have before me, it appears that he constructed an extremely large wooden scale beam supported by numerous braces, but free to be tilted in a vertical direction after the manner of all other scale beams. As this apparatus was of great weight and offered enormous resistance to the air, I do not understand how it was possible to obtain any very correct readings, especially as it was in the open and subject to every varying current of air. [Illustration: Fig. 32.--Machine with a rotating arm, 31·8 feet long, to which is attached the object to be experimented with. Professor Langley had a similar machine and called it a “whirling table.”] [Illustration: Fig. 33.--A screw and fabric covered aeroplane in position for testing.] [Illustration: Fig. 34.--The rotating arm of the machine with a screw and aeroplane attached.]