In 1849, the "interrupted thread" screw, for use in closing the breeches of guns was invented. Many men have claimed the honor of this invention. Regardless of who the particular inventor was, the invention itself must be regarded as one of a very high order, from the standpoints of originality, constructiveness and usefulness. Though the screw itself was a very old contrivance, the idea of cutting a long slot lengthwise, so that the screw could be pushed forward quickly without the slow process of continuously turning it around, yet so arranged that the screw could be turned when near the end of its travel, and the force-gaining power of the screw-thread thus secured, seems to have been entirely new. Certainly the idea was original and brilliant and useful. To develop the idea into a concrete plan was not difficult, and neither was it difficult to carry the concrete plan into execution. This invention falls into the happy class of which the stethoscope is typical, in which the idea originally conceived was so perfect, that little else was needed. The main use of this invention has been that for which it was first intended, to close the breeches of guns. It is used in most of the navies and armies. Its principal rival is the famous sliding breech-block of Krupp. In 1849, came an invention in the gun class, the magazine gun, made by Walter Hunt. This invention also seems to fulfil all the requirements of a real invention, in originality of conception, constructiveness of development and ultimate usefulness. But in this case, the original idea can hardly be declared as brilliant and spectacular as that of the "interrupted thread"; and certainly the labor of developing it was incomparably greater. The author feels the temptation of declaring that the more brilliant and valuable a conception is, the less will be the difficulty of developing it. He refuses to declare it, however, realizing that it would not be wholly true; and yet he wishes to point out that if a conception be wholly erroneous, it cannot be developed into any concrete plan whatever; and that many of the most brilliant conceptions, such as the fist-hammer, the flute, the telescope, the telegraph and the telephone were very easily developed into forms sufficiently concrete to make them practically usable. An idea itself is an extremely simple thing, even if it be developed ultimately into a highly complex machine. The idea of the steam engine, for instance, the idea which Hero conceived was, of itself, extremely simple; but see into what complex forms it has been developed! The original idea of Hero was easily developed into "Hero's engine." The improvements that have been made upon it have been the developments of separate ideas that were conceived later. Not one of these ideas has been nearly so brilliant as Hero's, and few of them have been so easily developed.