The experienced mechanic who reads the descriptions here given of the various devices which have been proposed for the construction of a perpetual-motion machine must be struck with the childish simplicity of the plans which have been offered; and those who will search the pages of the mechanical journals of the last century or who will examine the two closely printed volumes in which Mr. Dircks has collected almost everything of the kind, will be astonished at the sameness which prevails amongst the offerings of these would-be inventors. Amongst the hundreds, or, perhaps, thousands, of contrivances which have been described, there is probably not more than a dozen kinds which differ radically from each other; the same arrangement having been invented and re-invented over and over again. And one of the strange features of the case is that successive inventors seem to take no note of the failure of those predecessors who have brought forward precisely the same combination of parts under a very slightly different form. It is true that we occasionally find a very elaborate and apparently complicated machine, but in such cases it will be found, on close examination, to owe its apparent complexity to a mere multiplication of parts; no real inventive ingenuity is exhibited in any case. Another singular characteristic of almost all those who have devoted themselves to the search for a perpetual motion is their absolute confidence in the success of the plans which they have brought forth. So confident are they in the soundness of their views and so sure of the success of their schemes that they do not even take the trouble to test their plans but announce them as accomplished facts, and publish their sketches and descriptions as if the machine was already working without a hitch. Indeed, so far was one inventor carried away with this feeling of confidence in the success of his machine that he no longer allowed himself to be troubled with any doubts as to the machine's _going_ but was greatly puzzled as to what means he should take to _stop_ it after it had been set in motion! These facts, which are well known to all who have been brought into contact with this class of minds, explain many otherwise puzzling circumstances and enable us to place a proper value on assertions which, if not made so positively and by such apparently good authority, would be at once condemned as deliberate falsehoods. That falsehood, pure and simple, has formed the basis of a good many claims of this kind, there can be no doubt, but at the same time, it is probable that some of the claimants really deceived themselves and attributed to causes other than radical errors of theory, the fact that their machines would not continue to move.