Theodore Poesche has presented a plan for navigating tthe atmosphere with a car propelled by a steam engine without employing a balloon. His plan is published in the last number of the Journal of the Franklin Institute, and he has sent us a pamphlet containing his plan, illustrated with some engravings. We certainly would like to see Mr. Poesche driving his steam car " through the ether blue," but his plan presents no rational ground for us to hope we shall ever see him perform such a feat. We consider that safe, economical and successful aerial navigation would be the grandest and most important invention perhaps ever made, but no plan yet proposed, no means yet tried, have by actual experiments (the only way to test the value of any invention), proved anything more than that, with a gas more rarified than air, man is enabled to ascend by the help of a huge balloon to some upper strata of air, there to be drifted by the current of wind to some distant place —not without risk and danger in a single case. M. Poesche's plan is to build a long, narrow, and light wooden vessel, with a flat bottom, and with wings of canvas, and propel it by a screw propeller driven by steam power. " My ship," he says, " most nearly resembles the flying fish, which progresses by the spiral action of the tail, while its extended fins support it in the air." He trusts to the propeller to drive his long boat through the air, but he will find himself greatly mistaken. The screw was proposed long ago to drive aerial ships with balloons, but could not do it, and that it will be able to do so now without a balloon, is an impossibility, just as much so as that the author of the plan is able to fly by tying wings to his shoulders ; in fact, the latter case is the most feasible. There is one way to prove we are wrong, and that is for M. Poesche to put his invention into practice, and floor all opposition by actual demonstration.