The ship was lighted throughout by incandescent lamps, and there was even a small automatic piano worked by the electric current, on which popular airs could be played. If the gas and the gravity neutralizer worked as Professor Henderson hoped they would, as soon as the ship was completed, all that would be necessary to start on the voyage would be to fill the aluminum bag and set the air compressor in motion. The gas was made from common air, chemically treated and with a secret material added which by means of a complicated machine in a measure did away with the downward pull of the earth. Thus all that was necessary to carry on a long voyage was a quantity of gasolene to operate the engine which worked the electric machines, and some of this secret compound. The professor and his helpers had been working to good advantage. At last all was in readiness for the gas test. It was proposed to try it on an experimental scale. Some of the fluid was to be generated and forced into an aluminum cylinder under the same pressure it would be used in the air ship. To this cylinder were attached weights in proportion to the weight of the _Flying Mermaid_ with its load of human freight, engines and equipment. “This cylinder is just one one-hundredth the size of the cylinder of the ship,” said the professor. “I am going to fasten to it a hundred pound weight. If it lifts that our latest contrivance will be a success.” “You mean if the little cylinder pulls a hundred pounds up the big ship will take us and the machinery up?” asked Mark. “Certainly,” answered the professor. “If this cylinder lifts a hundred pounds, one a hundred times as big (as that of the _Mermaid_ is), will lift a hundred times as much, or ten thousand pounds. That is five tons, or more than a ton over what I figure to be the weight of our ship and contents. The latest war balloon can lift one ton with ease, and if my machine can not do five times as well I shall be disappointed.” The last adjustments were made, pipes were run from the gas generator to the cylinder, and the hundred pound weight was attached. “Everybody look out now,” said Mr. Henderson. “I am going to start the machine and let the gas enter the cylinder. It is a very powerful gas and may break the cylinder. If it does you must all duck.” The scientist gave a last look at everything. The boys got behind some boards whence they could see without being in danger. Washington, who had little fear so long as there was no danger of going under ground, took his place at the dynamo. Andy Sudds, with Bill and Tom, stationed themselves in safe places. “All ready!” called the professor.