a principle, a mere idea, but still no invention, in the proper sense of such a term, as applied to works of practical utility. All other early efforts were purely elementary or experimental. Let us take an illustration from another branch of science. It is not unreasonable to suppose that Electricity, using the term in its most extended sense, will some day or other supersede steam. We probably only require to be able to collect it cheaply and to control it effectually, to employ the artillery of heaven on the wide ocean, on our network of iron rails, and throughout all our manufacturing establishments. A, we will suppose, invents the first efficient Electric Engine, which with fifty horse power is fully at work; and in the course of a few years we sit down to write the history of this engine invented by A. Where shall we start in our history? Did not Faraday years ago produce an electro-magnetic engine; then of course Faraday invented A.’s engine! But we need not stop here; we have the whole history of electricity before us. There is no end of machines and engines; and a patent specification may come to light, the nearest possible thing to A. But we have not done yet, we have to consider France, &c., where we may find some more elementary electrical models before Faraday, and then of course before A. So that, on this system, as hitherto adopted, in attempting to settle a claim for De Caus, and depreciating the claim of the Marquis of Worcester, we may venture to predict an analogous fate for the Electric Engine, _hereafter_ to be invented by some inventor, A. Here we must plainly see that all that has hitherto been invented in this electrical line, does _not_ go beyond model or elementary apparatus, and that however nearly some of these may approach any plan hereafter to be invented, it would be ridiculous and highly reprehensible to set up claims based on _no_ practical value, and only colourably _similar_ in _some single particular_, but otherwise of no greater concern than as amusing or illustrative scientific toys. De Caus’ fountain was one of these pleasing toys, and De Caus himself could never have thought otherwise of it, taking his own large book and his own few lines of description; although it served the purpose of M. Arago to assume for it a pre-eminence over the Marquis of Worcester’s invention, merely because the latter came half a century later.