Many men combine to do constructive work of many kinds, and millions combine to work and fight together in armies; and it is an interesting fact that the working together of many men has been made possible by inventions, such as writing and printing. Yet there is hardly any other kind of work that is so wholly a "one man job" as inventing. The fact that only one man, as a rule, makes a certain invention, or writes a certain book, or composes a certain musical piece, or does any other inventional work, seems to spring naturally from the original fact that an invention begins with a picture made by imagination on a mind. Now a picture so made is an individual picture in an individual mind. If the picture is allowed to fade, or if from any cause the mind that received it does not form it into a definite entity, no invention is made. If, on the contrary, the mind develops the dim picture into a definite entity of some kind, that mind alone has made that invention; even if other minds improve it later by super-posing other inventions on it. It is true that sometimes a man who receives from his imagination a mental picture of some possible invention will communicate it to another man, and that other man will contribute some constructive work, and make the dim picture into a reality; so that the complete invention resulting will be the joint product of two men. It seems to be a fact, however, that these dim pictures have rarely been disclosed while in the formless period, and that almost every invention of which we know the history, was made by one man only. It need hardly be interjected here that we are discussing inventions only, and not the acts of making inventions practicable in the sense of making them useful or commercially successful. At the present day, there are few inventions indeed, which even after having been completed as inventions, need no modification at the hands of the engineer and the manufacturer, before they are suitable to be put to practical use. * * * * * That the Babylonians realized the importance of their invention is proved by the fact that their baked tablets were carefully preserved, and that in some cities large libraries were built in which they were kept, as books are kept in our libraries at the present day. When the expedition of the University of Pennsylvania made its excavations near the site of the ancient city of Nippur, in the southern part of Babylonia near the city of Babylon, a library was discovered that contained more than thirty thousand tablets. [Illustration: Early Babylonian Signs, Showing Their Pictorial Origin]