The analysis having been completed, the positions of the heavenly bodies at various times having been ascertained and tabulated, the next step would seem to be to construct a supposititious machine of which each part would represent a heavenly body, and in which those various parts would move according to laws induced tentatively from the actual motions of certain heavenly bodies. If it were afterwards found that all positions of each part, predicted in advance by applying the laws tentatively induced, corresponded to the actual positions of the heavenly body that it represented, then the supposititious machine could be truthfully declared to be a correct imitation of the great celestial machine. That is, the machine could be declared to be successful. The science of astronomy is, in effect, such a machine. Its parts are representations of the sun, moon and other heavenly bodies, that move according to laws that are illustrated in the diagrams, and expressed precisely in the formulas. The first act of the originator of the science of astronomy being one of the imagination in conceiving a picture of a celestial machine, and being like that of the inventor in conceiving a picture of an earthly machine; and his second act being also like that of the inventor in developing the picture, a justification for speaking of the "invention" of the science of astronomy may perhaps be reasonably claimed. (We must bear in mind, of course, that no invention is complete until the third act has been performed, and the thing invented has been actually produced.) To speak of invention in connection with bringing forth novel creations is far from new, for the phrases "construct a theory," "invent a science," "invent a religion," etc., are in almost daily use; and it may seem unnecessary to some persons, therefore, to discuss it at such length. But most people seem to regard such phrases as merely figurative; while the author wishes to make it plain that they are not figurative but exact.