One of our exchanges asserts that prepara tions are already in progress to contest the claim of Ericsson to the invention ofthe “ calo ric engine.” It also quotes from the “ London Mining Journal” of Nov. 6th, a paragraph ta ken from the Augsburg Gazette (a German paper,) which claims the invention for a ma gistrate named Prehn, of Lauenburg (Germa ny) who invented a caloric engine some years before Ericsson. It says:— ” By a series of costly experiments he suc ceeded in expanding and contracting air so ra pidly by alternately heating and cooling, as to prove its capability as a motive power. He, endeavored to get a patent for England, but found he should lay himself open to opposition and law suits; and although he obtained one for Berlin, and had testimonials of success from Macpherson and George frephenson, in England, Von Humboldt and Rapsold, of Ham burg, and Schumacher, of Altona, ill-success brought him to the grave, leaving a widow and seven children." Public journalists and mere literary men generally display a great amount of ignorance respecting the history of inventions. Some believe and assert that James Watt was the inventor of the steam engine, while steam had been applied to mo"l'e machinery before he was born. Some assert that Fitch, Fulton, or Symington were the first inventors of the steamboat, while a patent was taken out for such an application in 1736 by Jonathan Hulls. There is a great difference between an impro ver and an original inventor. The original invention rnay not be much, and an improve ment may be everything, and vice versa. The, caloric engine, about which so much is just now said, is simply the application of heated air to propel machinery, as a substitute for steam. Now this is no new application nor invention, and neither Prehn nor Ericsson are the first inventors, and it remains to be shown yet whether as an improvement the Ericsson engine will be anything more than has already been accomplished. In 1827, two brothers (one a clergyman, we believe,) named Stirling, in the city of Glasgow Scotland, took out a patent for a hot air engine, which was illustrated and described in “ Gal loway's History of the Steam Engine” in 1832 ; this patent was secured for the applica tion Ilf the heated air to propel machinery in a particular manner 25 years ago. This engine communicated motion to a piston by alternately heating a portion of air con nected with one side of the piston, and at the same time cooling that in connection with the other side. This was done by means of two air vessels, the one communicating with the upper and the other with the lower side of the piston. An air vessel was filled with thin plates of iron perforated with holes, or with pieces of brick, and the lower part of each air vessel was heated by a fire placed under it, pretty much the same as the Erics son engine. The Stirlings, however, did not claim hot air in) their patent specification, and the conclusion iii—they did not believe themselves to be the first inventors ; it is pro bable that they knew a patent had been- taken out in 1824 for an atmospheric engine, by E.&J. Prentice, Baltimore, Md., or the one with two cylinders byW. Willis, ofCharles- ton, S. C., in 1826; at any rate, the application of hot air to propel machinery is anything but a nsw invention. Ericsson took out his first pa tent in 1834, a long time ago, and the illus tration of his principle, as exhibited on page 60, last volume, Scientific American, appears to embrace the very principle of Stirling's, only the arrangement is not the same. The princi ple of the new caloric engine, which as assert ed, will make it successful and more economi cal than the steam engine is, that after the heated air has acted upon the piston, it is not lost—the heat is saved and applied over again. This very principle :s described as belonging to the Stirling engine, which was improved and patented twelve years ago. We are thus particular because we wish to let the public know distinctly that the “ hot air,” alias caloric, engine, is not a new nor untried invention, very different from what many have been led to believe by the numberless feuilletonists of our daily, weekly and monthly periodicals. Gas Engines.—Many accounts have lately been spread before the public, about the em ployment of ether, chloroform, carbonic acid gas and other gas engines, as substitutes for the steam engine. As far back as 1824, a pa tent was taken out by Samuel Brown, of Lon don for the United States, and Minus Ward, of Baltimore, took out one in 1827, for a gas and heated air engine. Thos. S. Brown obtained his English patent. in 1823. It was called a gas vacuum engine, and was actuated by the inflammation of hydrogen in a vessel contain ing a portion of atmospheric air sufficient for combustion. This created more sensation in 1826 in London, than the caloric engine now does here; it, however, was a failure. In 1825 the celebrated Brunei obtained a patent for employing carbonic acid gas as a motive agent after it had been reduced to a fluid by Humphrey Davy, but he did not test it, being satisfied, we suppose, that it would be more expensive than steam. Benjamin Che- verton, an English gentleman, who sometimes writes now for our London scientific cotempo- raries, obtained a patent in 1826, for an im proved carboni'c acid gas engine, but it, like Brunei's, amounted to nothing at all. A pa tent was taken out the same year (1826) by a Mr. Howard, for an ether-alcohol engine, which was identical in principle to the one said to be now invented by Mons. Tremblay, of France, for working with chloroform, which is a similar chemical agent. Gunpow der, smoke, and we do not know how many more substitutes have been proposed and tried as substitutes for the steam engine, not one of which has maintained the least semblance of a,decent competition. The reason why, we will endeavor to set forth next week.